[Fstarnb]

Fixes #5876

When heat of mixing is enabled, quadratic and quartic particle profiles reconstruct concentration from average and surface states. Applying the finite-volume gradient to those expressions uses incompatible radial discretizations and raises a ShapeError during model build.

Use the symbolic radial derivative when the concentration expression contains a spherical spatial variable. Keep the existing grad/inner calculation for Fickian profiles, which have no explicit radial variable.

This complements #5769: that PR adds phase summation, effective diffusivity, and the zero heat shortcut for uniform profiles. Its phase heat expression still applies grad(c), so the polynomial-profile build failure remains.

Validation

• Added build regressions for SPM and DFN with Fickian, quadratic, and quartic profiles; all six focused cases pass.
• Ruff check/format and all applicable changed-file pre-commit hooks pass.
• The full thermal test file also ran: the six new cases pass; six other solve tests fail locally at IDAKLU result extraction because this isolated environment installed pybammsolvers 0.10.0 while current main expects its 0.11.0 API. The full nox unit and documentation sessions were not run.