feat: allow custom HostFunctionsProvider in MerkleProof

[Farhad-Shabani]

Closes: #1147

Integration tests: informalsystems/basecoin-rs#174

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PR author checklist:

• Added changelog entry, using unclog.
• 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: Patch coverage is 41.42857% with 41 lines in your changes are missing coverage. Please review.

Project coverage is 63.79%. Comparing base (91bee67) to head (fdab306).

Files	Patch %	Lines
...lients/ics07-tendermint/src/client_state/common.rs	0.00%	27 Missing ⚠️
ibc-core/ics23-commitment/types/src/merkle.rs	0.00%	13 Missing ⚠️
ibc-clients/ics07-tendermint/types/src/header.rs	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1158      +/-   ##
==========================================
+ Coverage   63.76%   63.79%   +0.03%     
==========================================
  Files         219      219              
  Lines       21387    21391       +4     
==========================================
+ Hits        13638    13647       +9     
+ Misses       7749     7744       -5     

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[Farhad-Shabani]

Hey @mina86, See please changes in this PR meet your requirements?

This follows a similar approach we took for enabling a custom Tendermint Verifier. Meaning that, so far, we've been using a concrete HostFunctionsManager (as seen with the ProdVerifier), with this, you now have the option to introduce your custom object that implements the HostFunctionsProvider. However, admittedly, this requires defining a similar ClientState wrapper type on your end and implementing the ClientState traits using standalone functions under the ibc-client-tendermint crate. Following that, you should be able to inject your custom HostFunctionsManager here (same as the way a custom Tendermint verifier can be passed).

Note that to enable the ClientState newtype to be generic over the HostFunctionsProvider (And even perhaps over the TmVerifier), we need to devise a thoughtful solution that involves making adjustments in upstream libraries such as tendermint-rs and ics23 (like this), ensuring relevant changes keep the ibc-derive working, and as well, won’t cause disruptions for other users.

Therefore, take this as an interim solution. Let us know your thoughts. Happy to help in any way we can.

[mina86]

This appears to be sufficient for our needs.