feat(compiler): add evolution option support

[chaokunyang]

Why?

• Add a cross-language way to disable schema evolution for stable messages/structs to avoid compatible metadata overhead.
• Let IDL files set a default evolving behavior that generators and runtimes can honor consistently.

What does this PR do?

• Adds evolving to FDL/proto file options and message options, plus generator logic to compute the effective value.
• Emits evolving-disabled annotations/macros/decorators in codegen for C++, Go, Java, Python, and Rust (new @ForyObject and pyfory.dataclass support).
• Updates runtime type resolution to choose STRUCT vs COMPATIBLE_STRUCT (and named variants) based on the evolving flag; adds per-language tests for overrides and new IDL roundtrip cases.
• Updates schema evolution docs and compiler schema reference; removes the old type-system doc stub.

Related issues

#3099
#1017
#2906
#2982

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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