Fixes regex for fallback signatures

[kyscott18]

Description

Bug fix for fallback signatures. Previously, it was not consistent with the docs or types.

Additional Information

Before submitting this issue, please make sure you do the following.

• Read the contributing guide
• Added documentation related to the changes made.
• Added or updated tests (and snapshots) related to the changes made.

---

PR-Codex overview

The focus of this PR is to fix the regex for fallback signatures in the abitype package.

Detailed summary

• Updated regex for fallback signatures to include external and optional payable state mutability.
• Added tests to cover the new regex pattern.
• Improved accuracy in identifying fallback signatures.

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[changeset-bot]

🦋 Changeset detected

Latest commit: bf44fec

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
abitype	Patch

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Name	Status	Preview	Comments	Updated (UTC)
abitype	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Mar 2, 2024 10:20pm

[tmm]

Nice one!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.85%. Comparing base (6b2979f) to head (bf44fec).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #229      +/-   ##
==========================================
+ Coverage   99.83%   99.85%   +0.01%     
==========================================
  Files          26       26              
  Lines        6082     6083       +1     
  Branches      195      195              
==========================================
+ Hits         6072     6074       +2     
  Misses          8        8              
+ Partials        2        1       -1     

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