Enable optical photon track offloading from Geant4 to Celeritas

[Rashika-Gupta]

Enables optical track offloading by inserting intercepted Geant4 optical photon tracks into the Celeritas optical state

• Introduces LocalOpticalTrackOffload to intercept and buffer Geant4 optical photon tracks.
• Inserts buffered tracks into the Celeritas optical state via the DirectGeneratorAction.
• Enables optical track offload selection through OpticalTrackOffload, initialised during setup

[github-actions]

Test summary

 5 898 files   9 436 suites   8m 0s ⏱️
 1 733 tests  1 723 ✅  10 💤 0 ❌
30 620 runs  30 462 ✅ 158 💤 0 ❌

Results for commit b6fe580.