Additions to #177

[BradyPlanden]

This adds the following:

• update subplot trace width via additional DEFAULT_SUBPLOT_TRACE_OPTIONS variable
• dataset access method,
• remove square brackets from plots as per SI standard,
• updates quick plot for varying length signals,
• adds pybop.is_numeric function for checking input values
• restores design cost exception for optimisation

Encompasses #224. This PR is also a step towards fixing our current failing scheduled tests.

[codecov]

Codecov Report

Attention: Patch coverage is 88.41060% with 35 lines in your changes are missing coverage. Please review.

Project coverage is 94.19%. Comparing base (f9b10e8) to head (41cf0f8).

❗ Current head 41cf0f8 differs from pull request most recent head a479136. Consider uploading reports for the commit a479136 to get more accurate results

Files	Patch %	Lines
pybop/costs/_likelihoods.py	75.92%	13 Missing ⚠️
pybop/plotting/quick_plot.py	81.81%	4 Missing ⚠️
pybop/costs/fitting_costs.py	93.47%	3 Missing ⚠️
pybop/observers/observer.py	90.00%	3 Missing ⚠️
pybop/models/lithium_ion/echem_base.py	50.00%	2 Missing ⚠️
pybop/plotting/plot_convergence.py	77.77%	2 Missing ⚠️
pybop/plotting/plot_cost2d.py	93.10%	2 Missing ⚠️
pybop/plotting/plot_problem.py	86.66%	2 Missing ⚠️
pybop/costs/design_costs.py	95.23%	1 Missing ⚠️
pybop/plotting/plot_dataset.py	83.33%	1 Missing ⚠️
... and 2 more

Additional details and impacted files

@@                      Coverage Diff                      @@
##           177-plotting-capabilities     #198      +/-   ##
=============================================================
- Coverage                      94.61%   94.19%   -0.43%     
=============================================================
  Files                             35       36       +1     
  Lines                           1857     1997     +140     
=============================================================
+ Hits                            1757     1881     +124     
- Misses                           100      116      +16     

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[NicolaCourtier]

Looks ready to merge once the coverage is passing, thanks very much @BradyPlanden!