Add Stanford Research SR830 lock-in amplifier driver

Problem: The lab's SR830 DSP lock-in amplifier, reached over a Prologix GPIB-USB
adaptor, had no driver in PyHardwareLibrary.

Solution: Add SR830Device (and DebugSR830Device) combining PhysicalDevice,
AnalogInputStreamDevice, AnalogOutputDevice, PhaseLockedDetectionDevice, and
TriggerableDevice:
- Aux A/D inputs (OAUX?) via getAnalogVoltage(AuxInput); Aux D/A outputs (AUXV)
  via setAnalogVoltage(value, AuxOutput).
- Demodulated reads X/Y/R/theta (OUTP?/SNAP?), reference frequency (FREQ?), input
  source (ISRC), sensitivity (SENS) and time constant (OFLT) in physical units
  with nearest-step snapping.
- Buffered acquisition of the internal data buffer (DDEF/SRAT/SEND/REST/STRT/
  PAUS/SPTS?/TRCA?) via the AnalogInputStreamDevice primitives, with a
  StreamChannel enum and a SampleClock (internal rate vs external per-edge).
- Trigger via TSTR (setTriggerSource) and TRIG (softwareTrigger).
- doInitializeDevice self-discovers the Prologix among the connected FTDI adaptors
  by confirming *IDN? contains SR830, and pins the adaptor serial for reconnects.
- DebugSR830Device swaps in a DebugPrologixGPIBPort (an in-memory CommunicationPort
  that follows the readData/writeData structure) so all parse/validate paths run
  without hardware.

Verified against the lab SR830 (s/n 86552): tests/testSR830.py has 43 tests,
including 8 that talk to the real instrument (reads, aux out round-trip, buffered
acquisition, trigger) and skip cleanly when no SR830 is attached.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T2DmAfLHSiK1fb3PiXDyJP

Author: dccote

CHANGELOG.md

@@ -6,6 +6,34 @@ API changes can land even when the minor version is unchanged.
 
 ## [Unreleased]
 
+### Added
+- `SR830Device` (and `DebugSR830Device`): Stanford Research SR830 DSP lock-in
+  amplifier over a Prologix GPIB-USB controller. It combines several capabilities:
+  `AnalogInputStreamDevice` (the four rear-panel Aux A/D inputs via `OAUX?`, plus
+  hardware-timed buffered acquisition of the demodulated outputs from the internal
+  data buffer), `AnalogOutputDevice` (the four rear-panel Aux D/A outputs via
+  `AUXV`), `PhaseLockedDetectionDevice` (X/Y/R/theta, reference frequency, signal
+  input source, sensitivity, and time constant), and `TriggerableDevice` (the
+  rear-panel TRIG IN). Enums: `AuxInput`, `AuxOutput`, `StreamChannel`,
+  `InputSource`. `doInitializeDevice` self-discovers the Prologix among the
+  connected FTDI adaptors by confirming `*IDN?`, and pins the adaptor's serial.
+- `PrologixGPIBPort` (`hardwarelibrary/communication/`): a `SerialPort` subclass
+  that speaks the Prologix GPIB-USB controller `++` protocol. GPIB instruments
+  talk to it with the ordinary `readString`/`writeString` primitives; the `++read
+  eoi` handshake is encapsulated in its `readString`.
+- New DAQ capability contracts in `daq/daqdevice.py`: `PhaseLockedDetectionDevice`
+  (lock-in / phase-locked detection), `TriggerableDevice` with the `TriggerSource`
+  enum, and the `SampleClock` enum for stream sample clocking.
+
+### Changed
+- `AnalogInputStreamDevice`: the sample-rate parameter of
+  `configureStream`/`acquireWaveform` is renamed `scanRate` -> `sampleRate`.
+  `LabjackDevice.configureStream` keeps `scanRate` as a temporary deprecated
+  synonym for existing callers.
+- `LabjackDevice` now imports `u3` (LabJackPython) lazily at point of use, so
+  `import hardwarelibrary.daq` (and the new SR830 driver) works on hosts that do
+  not have LabJackPython installed.
+
 ## [1.3.3] - 2026-07-08
 
 ### Changed

hardwarelibrary/daq/__init__.py

@@ -3,5 +3,11 @@
 from .daqdevice import (
     AnalogInputDevice, AnalogOutputDevice, AnalogIODevice, AnalogInputStreamDevice,
     DigitalInputDevice, DigitalOutputDevice, DigitalIODevice,
+    PhaseLockedDetectionDevice, InputSource,
+    TriggerableDevice, TriggerSource, SampleClock,
 )
-from .labjackdevice import LabjackDevice, DebugLabjackDevice
+from .labjackdevice import LabjackDevice, DebugLabjackDevice
+from .sr830device import (
+    SR830Device, DebugSR830Device, DebugPrologixGPIBPort,
+    AuxInput, AuxOutput, StreamChannel,
+)