Add GroupedSPMe model

[NicolaCourtier]

Description

Add a grouped parameter version of the SPMe for parameter identification.

Issue reference

New feature

Review

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• Updated the CHANGELOG.md in reverse chronological order (newest at the top) with a concise description of the changes, including the PR number.
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[codecov]

Codecov Report

Attention: Patch coverage is 99.59677% with 1 line in your changes missing coverage. Please review.

Project coverage is 99.22%. Comparing base (c8b00e6) to head (87abcc3).
Report is 36 commits behind head on develop.

Files with missing lines	Patch %	Lines
pybop/models/lithium_ion/basic_SPMe.py	99.50%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #584      +/-   ##
===========================================
+ Coverage    99.08%   99.22%   +0.13%     
===========================================
  Files           52       57       +5     
  Lines         3605     4240     +635     
===========================================
+ Hits          3572     4207     +635     
  Misses          33       33              

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[NicolaCourtier]

This implementation works with input currents and EIS, but it can only reliably run an experiment without the double layer (i.e. not with {"surface form": "differential"}). We are not currently sure whether this issue is on the PyBOP or PyBaMM side.

[brosaplanella]

Looks good, just some comments!