Fix remaining derive hygiene edge cases

[ya7010]

Summary

• propagate deprecated enumerate warnings from named and tuple enum fields
• run enum-level custom validation for unit variants
• isolate generated bindings from user fields and statics, including raw identifiers
• make autoderef helper method names field-specific to avoid collisions with user-defined inherent methods
• add regression coverage for every reproduced failure

Red-to-green verification

Before the implementation changes, the new tests reproduced all four problems:

• the autoderef regression test silently bypassed min_length validation
• the unit enum regression test returned Ok(()) instead of the custom validation error
• both enum warning expansion tests lacked the expected deprecation tokens
• generated bindings failed to compile with E0530 and captured a user error_params static

The same tests pass after the fixes.

Verification

• cargo nextest run (331 passed)
• cargo nextest run --all-features (342 passed)
• cargo test --all-features
• cargo test --no-default-features
• cargo clippy -- -D warnings
• cargo fmt --all -- --check
• git diff --check