Add structural validation for bytecode cache blobs using the serialized
record layout. The decoder shares primitive helpers across cache
sections instead of duplicating flat parsing logic.
Reject bad magic values, unsupported versions, invalid enum tags, and
truncated sections before materialization. Bound sequence reads against
the remaining blob so malformed sidecars cannot force large allocations.
Add a versioned Rust bytecode cache writer for fully compiled programs.
The blob records executable bytecode, metadata tables, source maps,
exception handlers, nested function bytecode, and class blueprints
without materializing GC objects.
Expose the serialized blob through RustIntegration as an owned
ByteBuffer so Web-facing callers can store it as HTTP cache data.
