fix: support AssignmentExpression in userEvent setup detection

[y-hsgw]

Checks

• I have read the contributing guidelines.

Changes

• Add support for detecting userEvent instances assigned via AssignmentExpression.
• Move userEventInstanceNames into the create function scope to avoid cross-file caching issues.

Context

• no-node-access rule output false-positive warning for FireEvent after 7.5.4 #1038 (comment)
• [no-node-access] False positives for no-node-access #1057

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.48%. Comparing base (2e7e1b6) to head (9146a8d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1055      +/-   ##
==========================================
+ Coverage   96.46%   96.48%   +0.01%     
==========================================
  Files          50       50              
  Lines        2687     2700      +13     
  Branches     1112     1117       +5     
==========================================
+ Hits         2592     2605      +13     
  Misses         95       95              

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