* perf(state): skip response body on HEAD requests

* feat(symfony): add enable_head_request_optimization config flag

HEAD responses now omit some observable headers (Content-Length, per-item cache tags); per semver that is a backward-
incompatible behavior change, so this commit ships an opt-out flag — set `enable_head_request_optimization: false` to restore the
prior GET-equivalent behavior.

* fix(state): do not list HEAD in Allow header without GET operation