Address issues with Tabulator embed_content and optimize row expansion

[philippjfr]

• Do not expand all rows by default if embed_content=True
• Do not auto-reset expanded rows if embed_content
• Ensure expanded rows are rendered efficiently

Fixes #7361

[codecov]

Codecov Report

Attention: Patch coverage is 89.28571% with 3 lines in your changes missing coverage. Please review.

Project coverage is 82.21%. Comparing base (5ef8909) to head (5bb1908).
Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
panel/tests/ui/widgets/test_tabulator.py	78.57%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7364      +/-   ##
==========================================
- Coverage   82.21%   82.21%   -0.01%     
==========================================
  Files         337      337              
  Lines       50513    50545      +32     
==========================================
+ Hits        41530    41556      +26     
- Misses       8983     8989       +6     

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[hoxbro]

LGTM, I have added some nits comments.

[hoxbro]

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