fix: allow uppercase x usernames

[aditiharini]

Why is this change needed?

We currently disallow uppercase x usernames which are valid.

Merge Checklist

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PR-Codex overview

This PR focuses on updating the username validation regex to allow uppercase letters for Twitter usernames.

Detailed summary

• Modified the TWITTER_REGEX from /^[a-z0-9_]{0,15}$/ to /^[a-zA-Z0-9_]{0,15}$/ to permit uppercase letters in usernames.

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[changeset-bot]

🦋 Changeset detected

Latest commit: 39e642d

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

This PR includes changesets to release 2 packages

Name	Type
@farcaster/core	Patch
@farcaster/hub-nodejs	Patch

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Name	Status	Preview	Comments	Updated (UTC)
hub-monorepo	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jan 23, 2025 0:35am

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 34.94%. Comparing base (1880070) to head (39e642d).
Report is 471 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (1880070) and HEAD (39e642d). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (1880070)	HEAD (39e642d)
	2	1

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2491       +/-   ##
===========================================
- Coverage   74.05%   34.94%   -39.12%     
===========================================
  Files          99      146       +47     
  Lines        9425    26282    +16857     
  Branches     2097     9328     +7231     
===========================================
+ Hits         6980     9185     +2205     
- Misses       2327    14728    +12401     
- Partials      118     2369     +2251     

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