_calibrate_tas: allow selecting predictors

[mathause]

• Addresses Add ability to make realisations and train just from tas #19
• Tests added
• Passes isort . && black . && flake8
• Fully documented, including CHANGELOG.rst

This adds the use_tas2 and use_hfds keywords to _calibrate_tas which allows to set whether tas ** 2 and hfds are used for calibration. This would add some tests, however, these are slow ones and it adds some seconds to the test suite (see also #290). So I need to consider if I want to merge this...

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (70a6a0e) 86.99% compared to head (a2b4ed1) 86.89%.
Report is 1 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #291      +/-   ##
==========================================
- Coverage   86.99%   86.89%   -0.10%     
==========================================
  Files          38       38              
  Lines        1599     1580      -19     
==========================================
- Hits         1391     1373      -18     
+ Misses        208      207       -1     

Flag	Coverage Δ
unittests	86.89% <100.00%> (-0.10%)	⬇️

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Files	Coverage Δ
mesmer/calibrate_mesmer/calibrate_mesmer.py	92.56% <100.00%> (+1.38%)	⬆️

... and 11 files with indirect coverage changes

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