Improve Chrome importer marker payload logic

[canova]

Fixes #5715.

This PR does three things:

1. Puts the category properly to the marker categories.
2. Removes the dummy payload if the event doesn't have any data.
3. Removes beginEventDetail all together with all the logic around it.

It's a relatively small PR, but test changes make it look bigger.

Example chrome profile: Trace-20251212T152428.json.zip

Before / after

It looks like the chrome categories include commas, but this way still looked like an improvement to me.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review. :white_check_mark: Project coverage is 85.66%. Comparing base (38eb6ad) to head (b1f4716). :warning: Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/profile-logic/import/chrome.ts	95.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5717      +/-   ##
==========================================
+ Coverage   85.64%   85.66%   +0.01%     
==========================================
  Files         313      313              
  Lines       31013    31013              
  Branches     8449     8530      +81     
==========================================
+ Hits        26562    26566       +4     
+ Misses       4021     4017       -4     
  Partials      430      430              

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