Add fitting functionality for geometric parameters

[BradyPlanden]

This PR adds functionality to fit geometric parameters in pybop. This essentially requires a model rebuild every iteration, but a combined effort to minimise the number of objects that get rebuilt. It completes the following:

• Adds rebuild() method to base_model
• Adds functionality to classify and store parameters based on their type (requires rebuild or not) via model.rebuild_parameters
• Adds set_rebuild_parameters() to create the required dictionary of geometric parameters
• Adds a copy() method to base_model
• A type change to plot_cost2D()
• Adds tests needed for coverage

Closes #18

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (45df796) 94.58% compared to head (8a17a99) 94.70%.
Report is 17 commits behind head on develop.

Files	Patch %	Lines
pybop/models/base_model.py	93.87%	3 Missing ⚠️
pybop/_problem.py	91.66%	1 Missing ⚠️
pybop/parameters/parameter.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #169      +/-   ##
===========================================
+ Coverage    94.58%   94.70%   +0.11%     
===========================================
  Files           44       44              
  Lines         1829     1887      +58     
===========================================
+ Hits          1730     1787      +57     
- Misses          99      100       +1     

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[BradyPlanden]

Hi @NicolaCourtier, this should now be ready for review. I've updated the spm_CMAES.py example to be geometric as a reference. Seems to be working fine, and isn't a massive hit on performance.

[NicolaCourtier]

Did you mean to change spm_CMAES as well as add spm_geometric_parameters as a separate example? They look very similar to me. Great to hear that it's up to speed!

[NicolaCourtier]

Looks good to me, thanks @BradyPlanden, don't forget the Changelog!