Add PEP517/518 pyproject.toml support

[agriyakhetarpal]

Some of the key changes in this PR are as follows:

1. Declarative metadata via TOML tables
2. The ruff and pytest configurations are included in the newly-added pyproject.toml
3. distutils is deprecated, so I removed the setup.py shim file altogether considering that PyBOP in itself is a pure-Python package
4. Marked pybop.version as a private sub-module for pybop – this ensures that no one imports pybop.version.__version__ since the correct and intended way is through accessing pybop.__version__, which is unchanged except for the fact that the version is now defined in pyproject.toml; the good thing about this is that the package will now not have to be imported via import pybop to parse the version string

P.S. I should perhaps look at doing point 4 for PyBaMM too.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c72cf71) 94.57% compared to head (45df796) 94.58%.
Report is 15 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #203   +/-   ##
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  Coverage    94.57%   94.58%           
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  Files           44       44           
  Lines         1826     1829    +3     
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+ Hits          1727     1730    +3     
  Misses          99       99           

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[BradyPlanden]

Excellent, thanks for the contribution @agriyakhetarpal! Just one spot that's worth updating.