Add capability mixins to the power-meter family

[dccote]

Problem

PowerMeterDevice baked wavelength-calibration hooks directly into the base class even though not every meter calibrates by wavelength, and there was no way to introspect what a given meter can do. The laser-source family (hardwarelibrary/sources/) already models optional features as interface-segregated Capability mixins, but the power meters did not mirror that structure.

Solution

Introduce hardwarelibrary/powermeters/capabilities.py, a mirror of sources/capabilities.py, with a Capability ABC and three orthogonal mixins:

Mixin	Public API	do* hooks
WavelengthCalibratable	getCalibrationWavelength / setCalibrationWavelength	doGetCalibrationWavelength, doSetCalibrationWavelength
AutoScalable	autoScaleIsOn / turnAutoScaleOn / turnAutoScaleOff	doGetAutoScale, doTurnAutoScaleOn, doTurnAutoScaleOff
ScaleAdjustable	getScale / setScale / availableScales	doGetScale, doSetScale, doGetAvailableScales

• PowerMeterDevice now keeps only the always-present doGetAbsolutePower hook and gains capabilities() / hasCapability() introspection, copied from LaserSourceDevice.
• Wavelength hooks moved out of the base into WavelengthCalibratable.
• IntegraDevice and FieldMasterDevice declare WavelengthCalibratable; their existing hooks satisfy the contract unchanged. AutoScalable / ScaleAdjustable are left for future auto-ranging meters — no driver falsely advertises them.
• AutoScalable and ScaleAdjustable are kept fully orthogonal; a driver that needs "auto off before manual scale" handles it in its own doSetScale.

MRO / cooperative init (2nd commit)

Adding the mixins surfaced a latent init bug shared by the whole library. PhysicalDevice.__init__ did not call super().__init__(), and in the MRO of a device that mixes in a capability it sits ahead of the mixins:

IntegraDevice -> PowerMeterDevice -> PhysicalDevice -> WavelengthCalibratable -> Capability -> ABC -> object

So the init chain terminated at PhysicalDevice and a mixin's __init__ was never reached — mixins could only fake instance defaults with class attributes, and any future mixin holding real per-instance state would be silently skipped.

Fix:

• PhysicalDevice.__init__ now ends with super().__init__(), making it a cooperative base. It still consumes the device-identity arguments and forwards nothing, so the contract (documented on Capability) is: a mixin __init__ takes no required arguments and calls super().__init__() itself.
• WavelengthCalibratable / ScaleAdjustable now set their per-instance state (calibrationWavelength, scale) in a cooperative __init__ instead of shared class attributes.
• DebugFieldMasterDevice routes through super().__init__() instead of calling PhysicalDevice.__init__ directly, so it no longer skips PowerMeterDevice (absolutePower is now initialized to 0).

Verified safe for every multiply-inheriting device (Matisse, Millennia, Labjack, Cobolt, power meters) — none of their mixins define an __init__ to collide with.

Tests

Adds TestFieldMasterCapabilities covering capabilities() / hasCapability(), including that the driver class does not leak into the reported list. Existing wavelength tests now exercise the mixin. Full suite: 398 passed, 235 skipped, 0 failures.

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