Use project traces in plots

[dalonsoa]

Description

This replaces the previous method of calculating the traces at the plot level for the projects. Changes will follow to do the same for the user's capacity. Whatever traces are shown for the project information, they should be unchanged after this PR.

As a side effect, a few changes have been made to properly use the timezone - since otherwise some datetime objects created by pandas were naive.

Fixes #522

Type of change

• Documentation (non-breaking change that adds or improves the documentation)
• New feature (non-breaking change which adds functionality)
• Optimization (non-breaking, back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (whatever its nature)

Key checklist

• All tests pass (eg. python -m pytest)
• The documentation builds and looks OK (eg. mkdocs serve)
• Pre-commit hooks run successfully (eg. pre-commit run --all-files)

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added or an issue has been opened to tackle that in the future. (Indicate issue here: # (issue))

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.40%. Comparing base (55a100e) to head (a5c3db1).

Additional details and impacted files

@@                     Coverage Diff                      @@
##           630_sync_clockify_button     #650      +/-   ##
============================================================
+ Coverage                     92.28%   92.40%   +0.11%     
============================================================
  Files                            50       50              
  Lines                          1490     1487       -3     
  Branches                        113      111       -2     
============================================================
- Hits                           1375     1374       -1     
+ Misses                           97       96       -1     
+ Partials                         18       17       -1     

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