Support for PyBaMM v26.7

[DavidMStraub]

PyBaMM v26.7 introduces a couple of breaking changes.

This PR makes some minimal fixes:

• Use IDAKLUSolver as default
• Set voltage_as_state in SPM(e) models to preserve pure ODE behaviour for the moment (but see Add support for DAE models with PathSim solvers #18)
• Pin PyBaMM to the current minor version as upper bound to guard against unhandled breaking changes in future releases

[Copilot]

Pull request overview

Updates pathsim-batt to remain compatible with PyBaMM v26.7’s breaking solver/model-option changes, while keeping the ODE-only blocks working as before and guarding against future minor-version breakage.

Changes:

• Switch default PyBaMM build/discretisation solver to pybamm.IDAKLUSolver().
• Inject legacy SPM/SPMe options ("voltage as a state": "false", "surface form": "false") to keep ODE-only blocks operating on pure ODE systems under PyBaMM ≥ 26.7.
• Upper-bound PyBaMM dependency to <26.8 and update CI matrix to cover 26.7 plus older supported versions.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/pathsim_batt/cells/pybamm_cell.py	Generalizes option injection, forces legacy ODE discretisation for SPM/SPMe on PyBaMM 26.7+, and switches default solver to IDAKLU.
tests/cells/test_lead_acid.py	Clarifies why CasadiSolver is still used explicitly for LOQS co-sim on PyBaMM < 26.7.
README.md	Updates compatibility note about LOQS Jacobian behavior and solver selection across pinned PyBaMM versions.
pyproject.toml	Adds an upper bound on PyBaMM (<26.8) to prevent unvetted minor-version breaking changes.
.github/workflows/test.yml	Moves “latest” CI testing to PyBaMM 26.7 and extends the matrix to include 26.6 in the “older versions” coverage.

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