Set resource mode while bundling notebook assets

[philippjfr]

Two things:

1. Seemingly we never correctly applied the resource mode while bundling resources (which presumably had some effect on bundling resources for custom components)
2. We already had a context manager to handle it

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 87.07%. Comparing base (b2cb0c3) to head (136caa1).
Report is 1 commits behind head on main.

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

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7716   +/-   ##
=======================================
  Coverage   87.07%   87.07%           
=======================================
  Files         346      346           
  Lines       52675    52671    -4     
=======================================
  Hits        45865    45865           
+ Misses       6810     6806    -4     

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