Add assert_valid_signature utility

[utgarda]

Add assert_valid_signature utility and use it for signature validation
fixes #1223

Added assert_valid_signature utility function in packages/account/src/utils.cairo that:

• Standardizes signature validation using SRC6 is_valid_signature interface
• Includes backwards compatibility (checks both starknet::VALIDATED and 1)
• Takes signer address, hash, signature, and custom error message as parameters

Replaced duplicate signature validation logic in:

• SRC9 Component (src9.cairo) - Outside execution validation
• Governor Component (governor.cairo) - Vote casting by signature
• Votes Component (votes.cairo) - Delegation by signature
• ERC20 Component (erc20.cairo) - Permit function validation

Integration test coming

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.98%. Comparing base (a036924) to head (0fda783).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1444      +/-   ##
==========================================
+ Coverage   92.78%   92.98%   +0.19%     
==========================================
  Files          78       78              
  Lines        2093     2081      -12     
==========================================
- Hits         1942     1935       -7     
+ Misses        151      146       -5     

Files with missing lines	Coverage Δ
packages/account/src/extensions/src9/src9.cairo	95.00% <100.00%> (-0.66%)	⬇️
packages/account/src/utils.cairo	100.00% <100.00%> (+11.11%)	⬆️
packages/governance/src/governor/governor.cairo	92.54% <100.00%> (+2.01%)	⬆️
packages/governance/src/votes/votes.cairo	89.65% <100.00%> (-0.67%)	⬇️
packages/token/src/erc20/erc20.cairo	98.03% <100.00%> (-0.04%)	⬇️

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[ericnordelo]

Thanks @utgarda. Looking very good! I left a couple of comments, but it is almost ready.

[ericnordelo]

@immrsd, can you also review this PR before we merge it? Note that we may need to refactor the util outside of the account package when separating the interface package as discussed, but let's merge this in the meantime.