Run in parallel via CLI

[stefmolin]

Fixes #218
Fixes #274 (hopefully)

Describe your changes

• Switch from tqdm to rich for progress tracking
• Set up pytest-xdist to distribute tests over multiple CPU cores
• Reworked CLI to parallelize morphing over specified number of workers when there is more than one job and more than one worker requested. Passing 0 will use all available cores.
• Updated docs and test suite for new additions
• Set matplotlib backend to Agg in actions to hopefully fix tkinter issue on Windows runners

Checklist

• Test cases have been modified/added to cover any code changes.
• Docstrings have been modified/created for any code changes.
• All linting and formatting checks pass (see the contributing guidelines for more information).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.58%. Comparing base (ace8539) to head (f3b67af).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #273      +/-   ##
==========================================
+ Coverage   98.54%   98.58%   +0.03%     
==========================================
  Files          80       81       +1     
  Lines        1991     2043      +52     
  Branches      113      121       +8     
==========================================
+ Hits         1962     2014      +52     
  Misses         26       26              
  Partials        3        3              

Files with missing lines	Coverage Δ
src/data_morph/cli.py	100.00% <100.00%> (ø)
src/data_morph/morpher.py	100.00% <100.00%> (ø)
src/data_morph/progress.py	100.00% <100.00%> (ø)
tests/test_cli.py	100.00% <100.00%> (ø)
tests/test_morpher.py	100.00% <100.00%> (ø)