imp: further minimization of prost imports

[Farhad-Shabani]

Closes: #997
In continuation of: #998
Integration tests: informalsystems/basecoin-rs#147

Relevant context: #997 (comment)

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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: 19 lines in your changes are missing coverage. Please review.

Comparison is base (2259108) 70.90% compared to head (16f8e89) 70.86%.

Files	Patch %	Lines
ibc-clients/ics07-tendermint/src/client_state.rs	0.00%	4 Missing ⚠️
ibc-core/ics23-commitment/types/src/commitment.rs	25.00%	3 Missing ⚠️
ibc-core/ics23-commitment/types/src/merkle.rs	0.00%	3 Missing ⚠️
...it/src/testapp/ibc/clients/mock/consensus_state.rs	66.66%	3 Missing ⚠️
...clients/ics07-tendermint/types/src/client_state.rs	85.71%	1 Missing ⚠️
...ents/ics07-tendermint/types/src/consensus_state.rs	85.71%	1 Missing ⚠️
ibc-clients/ics07-tendermint/types/src/header.rs	85.71%	1 Missing ⚠️
...clients/ics07-tendermint/types/src/misbehaviour.rs	85.71%	1 Missing ⚠️
...stkit/src/testapp/ibc/clients/mock/client_state.rs	85.71%	1 Missing ⚠️
...stkit/src/testapp/ibc/clients/mock/misbehaviour.rs	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1000      +/-   ##
==========================================
- Coverage   70.90%   70.86%   -0.05%     
==========================================
  Files         178      178              
  Lines       17905    17869      -36     
==========================================
- Hits        12696    12663      -33     
+ Misses       5209     5206       -3     

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