fix(interpreter,rvm): correct partial object rule iteration and classification (#718)

Partial object rules with dynamic keys (e.g. `violations[k] if { ... }`)
only produced a single entry instead of collecting all bindings. Two
independent bugs caused this:

1. Interpreter: the early-return optimization in eval_output_expr_in_loop
   checked whether the rule_ref was constant but never verified whether
   the key expression was also constant. A variable key like `k` was
   treated as constant output, causing the loop to exit after the first
   iteration. Fixed by gating early-return on key_expr constness.

2. RVM: compute_rule_type incorrectly classified `p[k] if { ... }` as
   PartialSet instead of PartialObject. OPA v1 semantics define this
   form as a partial object (key -> true). Fixed the classification and
   added compiler error guards for patterns the RVM codegen cannot yet
   handle (constant keys, nested bracket keys), ensuring graceful
   fallback to the interpreter.

The OPA test harness now skips RVM validation per-case when partial
object compiler errors are raised, rather than blanket-skipping entire
folders. This preserves RVM coverage for unrelated tests in the same
folders.

Closes #712

Co-authored-by: Anand Krishnamoorthi <anakrish@microsoft.com>

tests/interpreter/cases/rule/partial_object_v1.yaml

@@ -0,0 +1,150 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+cases:
+  - note: constant_key_partial_object_v1
+    data: {}
+    input:
+      enabled: true
+    modules:
+      - |
+        package test
+        import rego.v1
+
+        p["fixed"] if {
+          input.enabled
+        }
+    query: data.test
+    want_result:
+      p:
+        fixed: true
+
+  - note: multilevel_partial_object_v1
+    data: {}
+    input:
+      nested:
+        app:
+          read: 1
+          write: 2
+        ops:
+          deploy: 3
+    modules:
+      - |
+        package test
+        import rego.v1
+
+        p[a][b] if {
+          some a, obj in input.nested
+          some b, _ in obj
+        }
+    query: data.test
+    want_result:
+      p:
+        app:
+          read: true
+          write: true
+        ops:
+          deploy: true
+
+  - note: constant_key_partial_object_explicit_value_v1
+    data: {}
+    input:
+      enabled: true
+    modules:
+      - |
+        package test
+        import rego.v1
+
+        p["fixed"] := 7 if {
+          input.enabled
+        }
+    query: data.test
+    want_result:
+      p:
+        fixed: 7
+
+  - note: multilevel_partial_object_explicit_value_v1
+    data: {}
+    input:
+      nested:
+        app:
+          read: 1
+          write: 2
+        ops:
+          deploy: 3
+    modules:
+      - |
+        package test
+        import rego.v1
+
+        p[a][b] := v if {
+          some a, obj in input.nested
+          some b, v in obj
+        }
+    query: data.test
+    want_result:
+      p:
+        app:
+          read: 1
+          write: 2
+        ops:
+          deploy: 3
+
+  - note: issue_712_reproducer_v0_partial_set
+    data: {}
+    input:
+      servers:
+        FOO: 1
+        BAR: 2
+        BAZ: 3
+    modules:
+      - |
+        package test
+        import future.keywords.in
+
+        violations[k] {
+          some k, _ in input.servers
+        }
+    query: data.test.violations
+    want_result:
+      set!: ["BAR", "BAZ", "FOO"]
+
+  - note: issue_712_reproducer_v1_partial_object
+    data: {}
+    input:
+      servers:
+        FOO: 1
+        BAR: 2
+        BAZ: 3
+    modules:
+      - |
+        package test
+        import rego.v1
+
+        violations[k] if {
+          some k, _ in input.servers
+        }
+    query: data.test.violations
+    want_result:
+      BAR: true
+      BAZ: true
+      FOO: true
+
+  - note: issue_712_reproducer_v1_contains_partial_set
+    data: {}
+    input:
+      servers:
+        FOO: 1
+        BAR: 2
+        BAZ: 3
+    modules:
+      - |
+        package test
+        import rego.v1
+
+        violations contains k if {
+          some k, _ in input.servers
+        }
+    query: data.test.violations
+    want_result:
+      set!: ["BAR", "BAZ", "FOO"]