fix: format abi item fallback formatting

[KedziaPawel]

fixes #253

As in the issue description, there were changes in the #229 for parseAbiItem, but there wasn't a corresponding change made for the formatAbiItem. This PR fixes that.

Also, I spotted that FallbackSignature type was only accepting fallback() external, and not fallback() external payable, which it should have, so I fixed that as it was a change related to the issue.

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PR-Codex overview

This PR focuses on enhancing the formatting of fallback functions in the formatAbiItem utility, ensuring that the output accurately reflects the stateMutability of the ABI items.

Detailed summary

• Updated expected values in tests to include external for fallback functions.
• Modified the formatAbiItem function to return fallback() external and fallback() external payable based on stateMutability.
• Added type checks to ensure correct formatting in TypeScript tests.

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🦋 Changeset detected

Latest commit: 7bc14de

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

This PR includes changesets to release 1 package

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abitype	Patch

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Name	Status	Preview	Comments	Updated (UTC)
abitype	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Dec 3, 2024 6:38pm

[Raiden1411]

Looks good to me but @tmm should have the final say on this

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.85%. Comparing base (ee60e67) to head (7bc14de).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #259   +/-   ##
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  Coverage   99.85%   99.85%           
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  Files          26       26           
  Lines        6103     6108    +5     
  Branches      186      188    +2     
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+ Hits         6094     6099    +5     
  Misses          8        8           
  Partials        1        1           

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