Fix onload handling in pyodide

[philippjfr]

Fixes #8053, Fixes #8074, Fixes #8094, Fixes #8103

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.37%. Comparing base (174aac0) to head (73ac6a4).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
panel/io/pyodide.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8174      +/-   ##
==========================================
- Coverage   87.38%   87.37%   -0.01%     
==========================================
  Files         348      348              
  Lines       53779    53787       +8     
==========================================
+ Hits        46994    46996       +2     
- Misses       6785     6791       +6     

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[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.