actix-http: play with allowing bytes passthrough in the h1 encoder

[asonix]

PR Type

?????Bug?????? (reduces memory use)

PR Checklist

• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• A changelog entry has been made for the appropriate packages.
• Format code with the latest stable rustfmt.
• (Team) Label with affected crates and semver status.

Overview

This is just me playing around with how to possibly avoid growing a persistent buffer to incredibly large sizes by allowing already-allocated Bytes types to pass through directly to IO in the h1 dispatcher

Comments very welcome

relates to #3367

[asonix]

I added a couple additional endpoints to the actix-web example in actix-http so I could run wrk against it

CPU: 12th Gen Intel(R) Core(TM) i5-12400
system: Linux firestar 6.9.1 #1-NixOS SMP PREEMPT_DYNAMIC Fri May 17 10:18:09 UTC 2024 x86_64 GNU/Linux

command: wrk -t12 -c400 -d30s $endpoint

for / and /medium performance is similar to the master branch
for /large performance is significantly improved

note that this isn't testing streaming bodies