Scaler ophyd-async device implementation

[Thomas Hopkins (thopkins32)]

Summary

Closes #287

Adds nslsii.ophyd_async.devices.scaler.Scaler:

• Scaler: the SynApps scalerRecord (e.g. a Struck SIS3820 run as a plain VME scaler): .CNT/.TP-driven step counting via trigger(), per-channel .Sn/.NMn/.PRn/.Gn readouts (num_channels, hinted_channels), and an optional SIS calc-record extension (num_calculations) for sites (HXN) that compute a derived scalar from the channels on the same IOC, in the same trigger cycle.

Here is how it is used:

scaler = Scaler("XF:99ID-ES{Sclr:1}", num_channels=8, hinted_channels=(2, 3))

Motivation / Context

Plain SynApps scaler records and the HXN SIS calc-record extension, and ad hoc retrying-read signal subclasses are independently reimplemented across csx, tes, xfm, fxi, srx, ios, and hxn profile collections. This consolidates them into one configurable pair of devices instead of each site's bespoke subclass.

I originally tried to implement the flyscanning ScalerMCS class but decided against it since it depends on a custom ZebraSaver IOC and otherwise does not follow the proper flyscanning protocol. To do this work would require a standard mechanism to write this data to disk (HDF writer or similar) and then use of StandardDetector and a data logic.

Testing

• Unit tests
• Integration tests with RE against a real/simulated IOC
• Tested at a beamline

References

SynApps / hardware

• SynApps scaler record: https://github.com/epics-modules/scaler
• Struck SIS3820 (manufacturer: Struck Innovative Systeme): https://www.struck.de/sis3820.htm

Beamline-specific implementations reviewed

Beamline	Source	Relevant behavior
CSX	90-softGluescalar.py	Scaler/FixedScalerCH pattern
TES	25-sclr.py	Byte-identical to CSX's 90-softGluescalar.py
XFM	20-scaler.py	Single device with a runtime mode='counting'/'flying' switch toggling read_attrs/configuration_attrs between a ScalerCH and a ScalerMCA sub-device — exactly the single-object, mode-switching design this PR deliberately avoids by keeping Scaler/ScalerMCS as two independent devices
SRX	30-scaler.py	SRXScaler, MCS fly-buffer usage, unpadded mca{1..32} naming
FXI	05-ion-chamber.py	FXIScaler, EpicsSignalROLazyier retry-on-stale-read subclass (obsoleted here by Format.UNCACHED_SIGNAL reads plus a trigger() that only completes once counting has actually finished)
IOS	20-detectors.py	DodgyEpicsScaler, same retry-on-stale-read motivation as FXI
HXN	22-scalers.py, hxntools/struck_scaler.py	StruckScaler/HxnTriggeringScaler, internal/external (modal) channel-advance triggering, SIS calc-record extension, Mca:{1..32}-style (colon) buffer naming