refactor: narrow secp256k1 verify signature branches

[Genmin]

Summary

• Narrow Secp256k1.verify before passing signatures to address recovery or public-key verification
• Avoid leaking the address/public-key OneOf union into recoverAddress, where yParity must be present
• Add a focused type/runtime regression covering recovered address verification and unrecovered public-key verification

Why

When verify destructures options before the branch check, TypeScript sees signature as a union of recovered and unrecovered signatures. The address branch passes that union to recoverAddress, which requires yParity, causing the optional/required mismatch reported downstream by viem users.

Related: wevm/viem#4379.

Validation

• pnpm check
• pnpm check:types
• pnpm test:types src/core/_test/Secp256k1.snap-d.ts
• pnpm test src/core/_test/Secp256k1.test.ts

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