Add a buffer pool on the network receiver side

[cBournhonesque]

The goal is to avoid allocating when we receive a packet, but instead re-use preallocated vectors that we can copy the packet bytes into.

However when I benchmarked it it didn't make any difference... Maybe because we're not receiving enough packets for it to make a difference in terms of allocations?

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

Attention: Patch coverage is 80.95238% with 8 lines in your changes missing coverage. Please review.

Project coverage is 66.90%. Comparing base (5558683) to head (1dcf257).
Report is 226 commits behind head on main.

Files with missing lines	Patch %	Lines
lightyear/src/utils/pool.rs	82.60%	4 Missing ⚠️
lightyear/src/connection/netcode/client.rs	66.66%	2 Missing ⚠️
lightyear/src/connection/local/client.rs	0.00%	1 Missing ⚠️
lightyear/src/connection/netcode/server.rs	85.71%	1 Missing ⚠️

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #435      +/-   ##
==========================================
- Coverage   66.91%   66.90%   -0.02%     
==========================================
  Files         160      160              
  Lines       10417    10445      +28     
==========================================
+ Hits         6971     6988      +17     
- Misses       3446     3457      +11     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.