CAS-14759: skip redundant normalizeprimarybeam() for cube+standard
For the standard gridder with specmode=cube, each worker in
CubeMajorCycleAlgorithm::task() already normalizes the primary beam
per-subcube during PSF making and writes the result back to the full
image. The subsequent master-side normalizeprimarybeam() loop over all
(pol x chan) planes was therefore redundant and, for a 7500-channel
8000x8000 cube, accounted for ~31 minutes of wall time after
"Time for making PSF and PB".
Changes:
- Extract the cube+standard guard into isCubeStandard bool for clarity.
- Skip the normalizeprimarybeam() loop when isCubeStandard is True.
- makePBCore() is unchanged and still skipped for cube+standard as before.
- Add a timing log entry "***Time for normalizeprimarybeam: <s> (skipped=<bool>)"
at INFO3 so the optimisation is observable in tclean logs.
This path is safe to skip only for standard+cube because mosaicft and
awproject gridders derive PB from sqrt(weight)/pbmax and require the
fully-assembled weight image, which is only available on the master
after all subcubes have been written back.
