PIPE-3085: Extend MS open optimization to `correctedampflag`, `rawflagchans`, `gcorfluxscale`
Hoist casa_tools.MSReader outside the inner loops in three additional
tasks, following the same pattern established for hif_applycal weblog
rendering:
- hif_correctedampflag: open once for the intent × field × spw loop
in _run_flagging_iteration; thread ms_handle through
_evaluate_heuristic → _evaluate_heuristic_for_baseline_set →
mstools.read_channel_averaged_data_from_ms.
- hif_rawflagchans: open once for the spw loop in
RawflagchansData.prepare; call openms.reset() between iterations
instead of opening a fresh handle per SPW.
- hifa_gfluxscale: open once for the field × spw loop in
_derive_calvis_flux; pass ms_handle to mstools.compute_mean_flux.
Also: bare except: → except Exception:, lazy % log formatting.
