Define a new validate_signer interface to enable customizable Signer validation across all handlers

[Farhad-Shabani]

Closes: #619

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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

Patch coverage: 92.42% and no project coverage change.

Comparison is base (ee1dbce) 73.07% compared to head (37ed081) 73.07%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #651   +/-   ##
=======================================
  Coverage   73.07%   73.07%           
=======================================
  Files         126      126           
  Lines       15678    15630   -48     
=======================================
- Hits        11456    11421   -35     
+ Misses       4222     4209   -13     

Impacted Files	Coverage Δ
crates/ibc/src/applications/transfer/error.rs	12.50% <ø> (+0.50%)	⬆️
crates/ibc/src/applications/transfer/packet.rs	52.63% <0.00%> (+9.15%)	⬆️
crates/ibc/src/core/context.rs	83.51% <ø> (ø)
crates/ibc/src/core/ics02_client/error.rs	20.83% <ø> (+0.83%)	⬆️
...tes/ibc/src/core/ics02_client/msgs/misbehaviour.rs	4.54% <0.00%> (ø)
crates/ibc/src/core/ics03_connection/error.rs	7.69% <ø> (+0.54%)	⬆️
crates/ibc/src/core/ics04_channel/error.rs	0.00% <ø> (ø)
...tes/ibc/src/applications/transfer/msgs/transfer.rs	46.66% <33.33%> (+0.87%)	⬆️
...ibc/src/core/ics02_client/handler/create_client.rs	82.89% <100.00%> (+1.20%)	⬆️
...ibc/src/core/ics02_client/handler/update_client.rs	95.12% <100.00%> (-0.12%)	⬇️
... and 36 more

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[plafer]

LGTM!

Please confirm you like the small changes I made