Validate DynamicMessage values before set

[fallintoplace]

Summary

• validate DynamicMessage::try_set values against the target field descriptor before mutation
• add a WrongValueKind reflection error for mismatched singular, repeated, map, and nested message values
• skip invalid stored values during encode so direct mutable field access cannot emit tag-only wire bytes

Tests

• cargo test -p buffa-descriptor --test dynamic_e2e --features reflect
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace --all-features

[github-actions]

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