proto: Add missing serde derives on Protobuf definitions

[romac]

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[mzabaluev]

Good, we'll need this in cometbft-rs too!
Before we can use the buf plugin to generate the majority of serde impls, that is.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 23.68421% with 29 lines in your changes are missing coverage. Please review.

Project coverage is 59.3%. Comparing base (99ed0b9) to head (acc17cc).
Report is 1 commits behind head on main.

❗ Current head acc17cc differs from pull request most recent head 8d01b40. Consider uploading reports for the commit 8d01b40 to get more accurate results

Files	Patch %	Lines
tendermint/src/private_key.rs	0.0%	10 Missing ⚠️
tendermint/src/crypto/ed25519/signing_key.rs	0.0%	6 Missing ⚠️
tools/proto-compiler/src/constants.rs	0.0%	6 Missing ⚠️
tendermint/src/public_key.rs	42.8%	4 Missing ⚠️
tendermint/src/crypto/ed25519/verification_key.rs	0.0%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1389     +/-   ##
=======================================
- Coverage   60.1%   59.3%   -0.8%     
=======================================
  Files        271     271             
  Lines      26221   26549    +328     
=======================================
- Hits       15768   15761      -7     
- Misses     10453   10788    +335     

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