perf: precalculate state mapper for mapping between experimental steps

[martinjrobins]

Description

Summary

Pre-calculate state mapper during simulation setup instead of on-demand at each step. performance gains mainly for smaller models (SPM)

Changes

File	Changes
base_model.py	New build_initial_state_mapper() method
simulation.py	Cache mapper during experiment setup
base_solver.py	Use cached mapper when available
test_simulation_with_experiment.py	Mapper validation tests

Benchmark Results (10 repeats)

Case	Setup	Solve 1	Solve 2	Total
CCCV · Chen2020 · DFN · CasadiSolver	-8.09%	-0.67%	-1.09%	-0.95%
CCCV · Chen2020 · DFN · IDAKLUSolver	-12.04%	+2.00%	+2.37%	+1.37%
CCCV · Chen2020 · SPM · CasadiSolver	+10.27%	+1.04%	+0.48%	+2.08%
CCCV · Chen2020 · SPM · IDAKLUSolver	+13.81%	-0.49%	+12.36%	+1.73%
CCCV · Marquis2019 · DFN · IDAKLUSolver	+0.82%	+0.48%	+1.70%	+0.58%
CCCV · Marquis2019 · SPM · CasadiSolver	-16.35%	+1.80%	+4.55%	+0.59%
CCCV · Marquis2019 · SPM · IDAKLUSolver	-5.81%	+2.43%	+10.43%	+1.89%
GITT · Chen2020 · DFN · CasadiSolver	-6.91%	+6.50%	+8.58%	+7.22%
GITT · Chen2020 · DFN · IDAKLUSolver	+2.27%	-1.08%	-5.93%	-1.84%
GITT · Chen2020 · SPM · CasadiSolver	+22.71%	+3.08%	+18.76%	+9.79%
GITT · Chen2020 · SPM · IDAKLUSolver	+1.90%	+6.95%	+19.84%	+7.63%
GITT · Marquis2019 · DFN · IDAKLUSolver	+3.06%	-0.95%	-5.91%	-1.61%
GITT · Marquis2019 · SPM · CasadiSolver	-14.97%	+9.40%	+19.61%	+9.30%
GITT · Marquis2019 · SPM · IDAKLUSolver	+12.25%	+0.15%	+20.21%	+4.51%
Average	+0.21%	+2.19%	+7.57%	+3.02%

Note: Positive values indicate speedup (mapper is faster). 10 repeats per case.

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #)

Important checks:

Please confirm the following before marking the PR as ready for review:

• No style issues: nox -s pre-commit
• All tests pass: nox -s tests
• The documentation builds: nox -s doctests
• Code is commented for hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

❌ Patch coverage is 90.38462% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.24%. Comparing base (ed711b6) to head (a50fb69).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pybamm/models/base_model.py	84.21%	6 Missing ⚠️
src/pybamm/simulation.py	93.10%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5380      +/-   ##
==========================================
- Coverage   98.30%   98.24%   -0.06%     
==========================================
  Files         328      328              
  Lines       28952    29052     +100     
==========================================
+ Hits        28460    28542      +82     
- Misses        492      510      +18     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[MarcBerliner]

Thanks Martin, this is a nice performance boost! Just some minor comments

[MarcBerliner]

Thanks @martinjrobins, looks good to me other than the doctest failure