Miscellaneous CI and Solution enhancements

[rkingsbury]

• Ensure more consistent column formatting in Solution.print()
• Switch math.log10 to np.log10 in Solution.p()
• Ensure Solution.p() always returns a regular float and returns np.nan if the concentration is zero or negative
• update pre-commit configuration
• use --dist loadscope in parallelized CI tests. Closes CI: parallel pytest execution causes intermittent test failures #170
• update license specification in pyproject.toml to conform to latest packaging standards - closes pyproject.toml License specification is out of date #233
• add py.typed to report type checking to other libraries. Closes CI: add py.typed for explicit type checking support #179

[codecov]

Codecov Report

❌ Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.90%. Comparing base (976167d) to head (e6dde9d).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pyEQL/solution.py	72.72%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #269   +/-   ##
=======================================
  Coverage   81.90%   81.90%           
=======================================
  Files           9        9           
  Lines        1503     1503           
  Branches      261      261           
=======================================
  Hits         1231     1231           
  Misses        226      226           
  Partials       46       46           

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