Utilise compact projections elsewhere in BeamTransfer

[jrs65]

From #107:

Separately, I can see a few ways to expand on this scheme that might improve performance elsewhere in the pipeline:

• Updating project_matrix_sky_to_telescope in the same way as your new project_vector_sky_to_telescope
• Only doing the "telescope SVD" on the BTM in the "compact representation" (with skipped frequencies and baselines removed), and updating the corresponding projection routines. This could potentially give some nice savings in runtime and memory usage for these SVDs