feat(rvm): extend program metadata and bump serialization to v6 (#654)

Add typed metadata support to RVM programs so that language frontends
can store language identity and arbitrary annotations alongside the
compiled bytecode.

Program metadata:
- Add `language` field to identify the source language (e.g. "rego",
  "azure_policy") so the VM can adjust semantics at runtime
- Add `annotations` map (BTreeMap<String, MetadataValue>) for
  frontend-specific key-value metadata
- Add MetadataValue enum with String, Bool, Integer, Float, Array,
  and Object variants, plus full serde support
- Add to_value() conversion for runtime access from VM instructions
- Add has_host_await flag with recompute_host_await_presence()

Serialization:
- Bump binary format version from 5 to 6
- Add JSON serialization for the new metadata fields

Assembly listing:
- Display language and annotations in the program header

Compiler:
- Track has_host_await during Rego compilation

src/languages/rego/compiler/core.rs

@@ -259,6 +259,9 @@ impl<'a> Compiler<'a> {
     }
 
     pub fn emit_instruction(&mut self, instruction: Instruction, span: &Span) {
+        if matches!(instruction, Instruction::HostAwait { .. }) {
+            self.program.has_host_await = true;
+        }
         self.program.instructions.push(instruction);
 
         let source_path = span.source.get_path().to_string();

src/languages/rego/compiler/mod.rs

@@ -23,8 +23,8 @@ pub use error::{CompilerError, Result, SpannedCompilerError};
 use crate::ast::ExprRef;
 use crate::lexer::Span;
 use crate::rvm::program::{Program, RuleType, SpanInfo};
-use crate::value::Value;
 use crate::CompiledPolicy;
+use crate::Value;
 use alloc::collections::{BTreeMap, BTreeSet};
 use alloc::string::String;
 use alloc::vec;