[WIP] CI: ImpactX Single Precision

[ax3l]

Add a runner for single precision tests in CI.

• make s-to-t / t-to-s transform more robust?
• make reduced beam characteristics more robust?
• adjust tolerances

[ax3l]

Looking at the t-to-s / s-to-t test in tests/python/test_transformation.py, which underlies the space charge implementation, I think that either that transformation or the ReducedBeamDiagnostics that we use to validate it need improvements to deal better with single precision.

We might be able to re-formulate/taylor the expressions in the transformations where we have terms like -1.0 + 1.000001 first:

• https://github.com/BLAST-ImpactX/impactx/blob/development/src/particles/transformation/ToFixedT.H
• https://github.com/BLAST-ImpactX/impactx/blob/development/src/particles/transformation/ToFixedS.H