refactor: change `Protocol`'s `Serialize` and `Deserialize` to use standard values

[davidhewitt]

Follow up from #2758

Changes

As noted in the above PR, the current implementation of Serialize and Deserialize for protocol will emit the enum name as it is read in source code. I propose it would be better to match the standard values in the spec, especially if #2758 is merged.

Merge requirement checklist

• [ ] CONTRIBUTING guidelines followed
• [ ] Unit tests added/updated (if applicable)
• [ ] Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• [ ] Changes in public API reviewed (if applicable)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.1%. Comparing base (1f0d9a9) to head (be812b2). Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2765   +/-   ##
=====================================
  Coverage   81.1%   81.1%           
=====================================
  Files        126     127    +1     
  Lines      24954   24964   +10     
=====================================
+ Hits       20255   20265   +10     
  Misses      4699    4699           

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[davidhewitt]

Thanks for the approval! Pushed a rebased commit, sorry for the delay.