fix: Allow null in InputChangeEvent value field

[GuillaumeRx]

This fixes an old issue where null is not allowed as a valid value in the InputChangeEvent

---

Note

Allow null for InputChangeEvent.value, add tests, update changelogs, and refresh example snap bundle shasums.

• SDK / Types:
  • Allow null in InputChangeEvent by making value nullable in InputChangeEventStruct (packages/snaps-sdk/src/types/handlers/user-input.ts).
  • Add unit test to validate null acceptance (packages/snaps-sdk/src/types/handlers/user-input.test.ts).
• Changelogs:
  • Note fix in packages/snaps-sdk/CHANGELOG.md and packages/snaps-execution-environments/CHANGELOG.md.
• Examples:
  • Update source.shasum for example snaps (packages/examples/packages/*/snap.manifest.json).

^{Written by Cursor Bugbot for commit c698209. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.28%. Comparing base (5a10086) to head (c698209).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3722   +/-   ##
=======================================
  Coverage   98.28%   98.28%           
=======================================
  Files         418      418           
  Lines       12152    12152           
  Branches     1876     1876           
=======================================
  Hits        11943    11943           
  Misses        209      209           

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