add bpms

[roussel-ryan]

This pull request adds and improves support for verifying and mapping Beam Position Monitor (BPM) process variables (PVs) in the BMAD virtual accelerator models. The main changes include enhancements to BPM element detection and mapping logic, as well as new tests to ensure BPM PVs are correctly exposed and mapped in the model.

BPM Support and Mapping Improvements:

• Modified get_variables in virtual_accelerator/bmad/variables.py to explicitly handle BPMs by name, ensuring they are treated as BPMs even if their device type is generic (Monitor).
• Updated get_tao_property in virtual_accelerator/bmad/cu_transformer.py to support returning BPM X and Y orbit positions (converted from meters to millimeters).

Testing Enhancements:

• Added assert_bpm_pvs_match_tao_lattice utility in virtual_accelerator/tests/_bmad_model_test_utils.py to verify that all BPM lattice elements have corresponding PV mappings and that expected BPM PVs are present in the model's supported variables.
• Integrated the new BPM assertion utility into the test suites for both CU-HXR and FACET models (test_cu_hxr.py and test_facet.py), adding dedicated tests to check BPM PV mappings. [1] [2] [3] [4]