fix: Message sending GC allocations

[EmandM]

Purpose of this PR

Fixes some GC allocations in message hot paths.

Jira ticket

fixes: #4091

Changelog

• Fixed: Resolved GC allocations in some hot paths

Documentation

• No documentation changes or additions were necessary.

Testing & QA (How your changes can be verified during release Playtest)

Functional Testing

Manual testing :

• Manual testing done

Automated tests:

• Covered by existing automated tests
• Covered by new automated tests

Does the change require QA team to:

• Review automated tests?
• Execute manual tests?
• Provide feedback about the PR?

If any boxes above are checked the QA team will be automatically added as a PR reviewer.

Up-port

Up-port needed

Backports

n/a

[codecov-github-com]

Codecov Report

Attention: Patch coverage is 86.66667% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...eobjects/Runtime/Messaging/Messages/RpcMessages.cs	0.00%	2 Missing ⚠️
...Runtime/NetworkVariable/Collections/NetworkList.cs	80.00%	2 Missing ⚠️

@@                Coverage Diff                @@
##           develop-2.0.0    #4119      +/-   ##
=================================================
+ Coverage          73.93%   73.94%   +0.01%     
=================================================
  Files                172      172              
  Lines              28095    28099       +4     
=================================================
+ Hits               20771    20777       +6     
+ Misses              7324     7322       -2     

Flag	Coverage Δ
NGOv2_project_testproject_ubuntu_pinnedTrunk	73.26% <86.66%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
.../Messaging/Messages/NetworkVariableDeltaMessage.cs	77.92% <100.00%> (ø)
...objects/Runtime/Messaging/NetworkMessageManager.cs	82.39% <100.00%> (ø)
...netcode.gameobjects/Runtime/Metrics/MetricHooks.cs	100.00% <100.00%> (ø)
...ode.gameobjects/Runtime/Serialization/BitReader.cs	94.23% <100.00%> (ø)
...eobjects/Runtime/Serialization/FastBufferReader.cs	80.03% <100.00%> (ø)
...eobjects/Runtime/Messaging/Messages/RpcMessages.cs	42.61% <0.00%> (+0.94%)	⬆️
...Runtime/NetworkVariable/Collections/NetworkList.cs	79.15% <80.00%> (-0.67%)	⬇️

Components	Coverage Δ
com.unity.netcode.gameobjects	73.94% <86.66%> (+0.01%)	⬆️

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