feat: add Azure Policy builtins with YAML test suite (#630)

* feat: add Azure Policy builtins with YAML test suite

Implement ARM template functions for Azure Policy evaluation:

Builtins:
- String: indexOf, lastIndexOf, trim, format, split, startsWith, endsWith,
  padLeft, concat, replace, toLower, toUpper, substring, guid, uniqueString
- DateTime: dateTimeAdd, dateTimeFromEpoch, dateTimeToEpoch, addDays
- Collection: intersection, union, take, skip, first, last, min, max,
  range, items, tryGet, tryIndexFromEnd, empty, array, createObject
- Encoding: base64, base64ToString, base64ToJson, uri, uriComponent,
  uriComponentToString, dataUri, dataUriToString
- Numeric: int, float, intDiv, intMod
- Misc: json, join, bool, string, coalesce, if, getParameter, resolveField
- Logic: logicAll, logicAny

Key implementation details:
- Unicode case-insensitive search via ICU4X case folding with single-pass
  fold_with_char_map() for indexOf/lastIndexOf
- .NET composite formatting (System.String.Format) with alignment, standard
  and custom datetime format specifiers, numeric format specifiers
- DateTime round-trip preserves input shape (Z vs +00:00, T vs space,
  fractional seconds) when no explicit output format is supplied
- Zero-cost as_str() helper borrows directly from Value::String(Rc<str>)
- BTreeSet<&Value> in array union avoids redundant cloning

Test suite:
- 53 YAML test files exercising all builtins via direct BUILTINS registry
- Coverage for edge cases: empty inputs, Unicode, fractional seconds,
  invalid alignment, unknown format specifiers, RFC3339 offset shapes

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

* fix: address PR review comments

- Fix percent_encode to only uppercase hex digits, not entire string
- Remove guid/uniqueString (unsupported); delete custom SHA-1 impl
- Replace unwrap_or(0) with proper error in format placeholder parsing
- Hoist CaseMapper into static CaseMapperBorrowed for zero per-call overhead
- Pre-allocate Vec in range() with_capacity
- Update bindings/ffi and bindings/ruby Cargo.lock
- Fix uri_component test expectations for correct case preservation

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

* fix: address second round of PR review comments

- float(): return Undefined when as_f64() fails instead of leaking
  the original non-f64 representation
- createObject(): reject odd number of arguments with an error
  (ARM-template parity)
- format(): error on unknown numeric format specifiers instead of
  silently passing through (matches .NET FormatException behavior)
- format(): cap alignment width at 10,000 to prevent DoS from
  user-controlled format strings like {0,1000000000}
- Add YAML test cases for all new error behaviors

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

* fix: address third round of PR review comments

- percent_decode: reject incomplete % escapes (e.g. "%", "%2") instead
  of treating them as literal characters
- parse_iso8601_duration: reject leftover digits without a unit designator
  at T boundary and end-of-input (e.g. "P1", "P1T2H")
- yaml_to_value: panic on unsupported YAML numeric representations instead
  of silently mapping to Null
- Revert unused src/languages/mod.rs changes (module is defined inline in
  lib.rs)

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

* fix: add missing edge-case tests and fix empty-delimiter panic

- fn_split: return input as single-element array for empty string
  delimiter instead of panicking (Rust's str::split("") panics)
- format: add test for F3 higher precision ({0:F3} + 1.23456 → 1.235)
- format: add test for N2 float with thousands separator
- format: add test for negative index error ({-1})
- split: add test for empty-string delimiter
- uri: add tests for query string and fragment in relative URI
- createObject: add test for non-string (numeric) keys

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

* fix: address fourth round of PR review comments

- Add MAX_VARIADIC_ARGS (64) constant for variadic builtin arity
  instead of registering with 0 (logic_all, logic_any, min, max,
  format, intersection, union, coalesce, createObject); set
  dateTimeAdd to exact arity 3

- Switch indexOf/lastIndexOf to UTF-16 code-unit indices to match
  .NET String.IndexOf semantics (track ch.len_utf16() in
  fold_with_char_map, use encode_utf16().count() for empty-needle
  lastIndexOf)

- Use DateTime::<Utc>::from_timestamp for explicit timezone type

- Remove stale docs/azure-policy/casing.md link from module doc

- Fix misleading comment in want_error test branch (code bails on
  Undefined, not accepts it)

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

---------

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

bindings/ffi/Cargo.lock

@@ -450,6 +450,28 @@ dependencies = [
  "cc",
 ]
 
+[[package]]
+name = "icu_casemap"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d4ca9983e8bf51223c2f89014fa4eaa9e9b336c47f3af0d000538f86f841fba1"
+dependencies = [
+ "icu_casemap_data",
+ "icu_collections",
+ "icu_locale_core",
+ "icu_properties",
+ "icu_provider",
+ "potential_utf",
+ "writeable",
+ "zerovec",
+]
+
+[[package]]
+name = "icu_casemap_data"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "98d4663d0f99b301033a19e0acf94e9d2fa4b107638580165e5a6ccc49ad1450"
+
 [[package]]
 name = "icu_collections"
 version = "2.1.1"
@@ -458,6 +480,7 @@ checksum = "4c6b649701667bbe825c3b7e6388cb521c23d88644678e83c0c4d0a621a34b43"
 dependencies = [
  "displaydoc",
  "potential_utf",
+ "serde",
  "yoke",
  "zerofrom",
  "zerovec",
@@ -471,6 +494,7 @@ checksum = "edba7861004dd3714265b4db54a3c390e880ab658fec5f7db895fae2046b5bb6"
 dependencies = [
  "displaydoc",
  "litemap",
+ "serde",
  "tinystr",
  "writeable",
  "zerovec",
@@ -524,6 +548,8 @@ checksum = "85962cf0ce02e1e0a629cc34e7ca3e373ce20dda4c4d7294bbd0bf1fdb59e614"
 dependencies = [
  "displaydoc",
  "icu_locale_core",
+ "serde",
+ "stable_deref_trait",
  "writeable",
  "yoke",
  "zerofrom",
@@ -840,6 +866,8 @@ version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b73949432f5e2a09657003c25bca5e19a0e9c84f8058ca374f49e0ebe605af77"
 dependencies = [
+ "serde_core",
+ "writeable",
  "zerovec",
 ]
 
@@ -987,6 +1015,7 @@ dependencies = [
  "dashmap",
  "data-encoding",
  "globset",
+ "icu_casemap",
  "indexmap",
  "ipnet",
  "jsonschema",
@@ -1235,6 +1264,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "42d3e9c45c09de15d06dd8acf5f4e0e399e85927b7f00711024eb7ae10fa4869"
 dependencies = [
  "displaydoc",
+ "serde_core",
  "zerovec",
 ]
 
@@ -1569,6 +1599,7 @@ version = "0.11.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6c28719294829477f525be0186d13efa9a3c602f7ec202ca9e353d310fb9a002"
 dependencies = [
+ "serde",
  "yoke",
  "zerofrom",
  "zerovec-derive",