perf(dispatch): route/method decision before full body read for 404/405 fast-fail #71

Context

Rust dispatcher currently reads full request body before route/method resolution in many paths. This increases cost for invalid endpoints/methods and enables cheap high-volume junk traffic to force unnecessary body buffering.

Current code

• src/dispatch.rs reads protocol body first, then computes route outcome and 404/405 handling.

Goal

Move route/method match decision earlier so 404/405 can fail fast without reading full body.

Desired behavior

• For non-matching paths/methods: return 404/405 early, avoid body read.
• For matched routes: preserve existing body-read semantics and size checks.

Acceptance criteria

• Dispatcher computes 404/405 before body consumption when possible.
• No functional regression in current tests.
• Add/extend tests proving body is not consumed in 404/405 cases (or equivalent behavioral proof).

Notes

This is primarily performance + robustness hardening; no API change intended.