imp: minimize prost dependency

[Farhad-Shabani]

Closes: #997

Integration tests: informalsystems/basecoin-rs#147

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PR author checklist:

• Added changelog entry, using unclog.
• Added tests.
• Linked to GitHub issue.
• Updated code comments and documentation (e.g., docs/).
• Tagged one reviewer who will be the one responsible for shepherding this PR.

Reviewer checklist:

• Reviewed Files changed in the GitHub PR explorer.
• Manually tested (in case integration/unit/mock tests are absent).

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (fe9a26b) 70.86% compared to head (f172a56) 70.90%.

Files	Patch %	Lines
ibc-clients/ics07-tendermint/src/client_state.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #998      +/-   ##
==========================================
+ Coverage   70.86%   70.90%   +0.04%     
==========================================
  Files         178      178              
  Lines       17918    17905      -13     
==========================================
- Hits        12698    12696       -2     
+ Misses       5220     5209      -11     

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