Improve test coverage

[elichad]

Broad improvements needed to coverage:

• Unit tests
• Integration tests
• Include Windows in CI

Specific improvements to existing tests:

• use TestCase.assertRaises with a specific exception type/message instead of catching/printing all Exceptions
• Split existing tests into smaller units

[elichad]

use TestCase.assertRaises with a specific exception type/message instead of catching/printing all Exceptions

[elichad]

Split existing tests into smaller units

[patrick-austin]

Updating with WIP information from #83

Notable uncovered areas

In addition to numerous exceptions and minor branches that are not covered (i.e. raising an exception if a file that should always be present is missing), the following areas have functional code that is currently untested but could be:

• io/uep.py from the coverage looks like second half of run() is never reached - also complicated by the fact this is being used to mock the calc attribute for ASE atoms, needs further analysis, see also Risk of infinite recursion in UEPCalculator.read #90
• quantum/vibrational/average.py "montecarlo" branch, dftb_pbc branch, castep branch...
• schemas.py some validations not tested

DFTB tests don't run, as _RUN_DFTB is hardcoded False. Haven't looked into this too much yet. Don't know if it's more feasible to try and install DFTB+ on the GHA runners or try and increase coverage by unit testing the following (currently uncovered) functions:

• io/output.py:write_phonon_reports
• quantum/main.py:asephonons_entry
• quantum/vibrational/phonons.py:ase_phonons_calc

The following files have no coverage, and are not called anywhere else in the codebase. Could write tests for them, but is it worth it for code that is never used? May have value as library functions but it's not obvious to me if they do.

Following discussion with @leandro-liborio will keep the following:

• calculate/uep/charged.py:ChargeDistrubution.Hfine
• dipolar/field.py

And remove the following:

• io/output.py:write_tensors
• quantum/grid.py
• quantum/reports.py
• utils.py:create_plane_grid