…… (backport #75) (#80)

* perf: Micro optimization to save one allocation per packet (backport cometbft#3018) (cometbft#3023)

This PR is a slight optimization to save one allocation per packet. We
have much more worthwhile performance improvements to pursue, just
driveby noticed it as I was reading through the code. (Though I am
surprised this did add up to 1 second in total -- 4% of the processing
time)

This re-uses the byte reader's allocation across all ReadMsg's. There is
no concurrenct access possible under safe usage (also implied by the
reader)

This is the cause of the 1s time on the far right:

![image](https://github.com/cometbft/cometbft/assets/6440154/d6c6bfaa-d287-4355-b094-9bdcbc6379c8)

---

#### PR checklist

- [x] Tests written/updated - covered by existing tests
- [x] Changelog entry added in `.changelog` (we use
[unclog](https://github.com/informalsystems/unclog) to manage our
changelog)
- [x] Updated relevant documentation (`docs/` or `spec/`) and code
comments
- [x] Title follows the [Conventional
Commits](https://www.conventionalcommits.org/en/v1.0.0/) spec
<hr>This is an automatic backport of pull request cometbft#3018 done by
[Mergify](https://mergify.com).

---------

Co-authored-by: Dev Ojha <ValarDragon@users.noreply.github.com>
Co-authored-by: Anton Kaliaev <anton.kalyaev@gmail.com>
(cherry picked from commit ad8f851)

* changelog

(cherry picked from commit dd19cb0)

# Conflicts:
#	CHANGELOG.md

---------

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
Co-authored-by: Dev Ojha <dojha@berkeley.edu>
Co-authored-by: PaddyMc <paddymchale@hotmail.com>