fix TS2683 false positives in nested Effect.gen

[mattiamanzati]

Summary

• avoid eager data-first signature analysis for problematic Effect contexts that can destabilize this typing in Effect.gen({ self: this }, ...)
• remove the unused eager EffectGenCallResult return-type caching and keep coverage by asserting through native effect-v4 fixtures and baselines
• add regression coverage for all reported #179 examples under strict mode, including nested generic calls, callback thunks, callee this, .pipe() chains, and curried wrappers

Fixes #179.

Validation

• pnpm setup-repo
• pnpm lint
• pnpm check
• pnpm test