feat(compiler): use generated hash for generated class as name

[chaokunyang]

Why?

• Align IDL auto-ID handling to use stable 32-bit hash names rather than numeric IDs when IDs are auto-generated.
• Update meta string EXTENDED payload handling for number strings across languages.

What does this PR do?

• Add package ... alias ... parsing and propagate the alias through schema/validators; compute auto IDs for messages/unions/enums using a 32-bit Murmur hash of namespace.type (alias-aware) and detect collisions.
• Change code generators to register auto-ID types by name (empty namespace + hash string) and treat auto-ID types as NAMED types in union type IDs; update registration comments.
• Refresh meta string encoding/decoding across runtimes (EXTENDED payload byte, number-string handling, zero-length optimization) and update related tests.
• Fix C++ TypeMeta name serialization to use meta string encoders and align Dart/Rust/Go tests/build paths with the updated encoding.
• Update compiler and protocol docs, regenerate IDL fixtures, and extend IDL round-trip tests (including enum coverage).

Related issues

#3099

Does this PR introduce any user-facing change?

• Does this PR introduce any public API change?
• Does this PR introduce any binary protocol compatibility change?

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