Improve fluo Fastify native route performance

[ayden94]

Recent local benchmark analysis shows fluo+Fastify is slower than Nest+Fastify on GET/query/route-heavy scenarios while JSON POST and Bun paths are not the main problem.

Observed directional numbers:

• read-search-local: Nest+Fastify 25,405 req/s, fluo+Fastify 16,351 req/s, fluo+Bun 24,397 req/s.
• rest-route-mix-local: Nest+Fastify 44,869 req/s, fluo+Fastify 31,760 req/s, fluo+Bun 43,003 req/s.
• json-command-local: Nest+Fastify 25,976 req/s, fluo+Fastify 29,384 req/s, fluo+Bun 39,448 req/s.

Scope:

• Focus on Fastify native eligible GET/query/route-heavy hot path.
• Preserve route matching, versioning, lifecycle, headers, request IDs, serializer behavior, multipart/rawBody fallback, middleware, guards, interceptors, and request-scoped DI.
• Use short benchmark loops while iterating, then a final 3-run confidence benchmark.

Acceptance:

• Same-worktree baseline captured before changes.
• Candidate retained only if read-search-local or rest-route-mix-local improves at least 5% and json-command-local does not regress more than 5%.
• Final benchmark improves at least one target GET scenario by 8% with no scenario regressing more than 5%.
• Public package changes include a changeset.