types!: port passport to registration-scoped typing model

[mcollina]

Summary

Port @fastify/passport to the registration-scoped typing model and complete a
strict test/type cleanup.

Highlights:

• registration-scoped typing across authenticator/route/strategy surfaces;
• request/reply/session handling tightened with explicit helper types;
• removal of unsafe double-casts (as unknown as) and broad any usage in TS
  source/tests;
• secure-session manager fix for session regeneration path (avoid stale session
  reference after regenerate);
• final validation state without test compat bridge and without skipLibCheck.

Dependencies

This PR is part of the migration stack and depends on:

• types!: remove declaration-merging reliance with registration-scoped decorator typing fastify#6581 (feat/typed-decorators)
• types!: add createPlugin helper for registration-scoped typing fastify-plugin#282 (feat/create-plugin)
• types!: port flash to registration-scoped typing model fastify-flash#145 (flash port in same typing model)

Validation

• npm run lint ✅
• npm run build ✅
• npm run build:test ✅
• npm test ✅

Context

Refs fastify/fastify#5061.