perf(ext/node): optimize node:http header matching (#34484)
## Summary
- Optimizes node:http request header processing by reducing hot-path
overhead in known-header matching.
- Preserves Node-compatible header semantics and raw header behavior
while keeping the change focused to request header materialization.
## Validation
- Ran focused node:http correctness coverage for request header
behavior.
- Ran paired release-lite throughput benchmarks on the same execution
target for control and header-heavy workloads.
- Confirmed the header workload improvement is outside observed
benchmark noise with neutral control results.
Co-authored-by: Nathan Whitaker <nathan@deno.com>
