Refactor: instruments have sensors

[j-atkins]

Overview

This PR centralises/abstracts instrument sensor/variable sampling logic so that each instrument declares which sensors it carries (e.g. TEMPERATURE, SALINITY, VELOCITY). Users can configure which sensors are active for each instrument in the expedition YAML.

This helps pave the way for easy addition of BGC sensors to the Argo float in a future PR (#234), and consolidation of CTD + CTD_BGC into a single instrument (#260) with a combined sensor allowlist. Also makes it straightforward to add new sensors to any instrument in the future (e.g., #312, #313), and streamlines them process for developers to add new instruments (i.e. #237)

Major changes

• sensors.py in instruments/ defines the SensorType class and per-instrument allowlists (so that there is control over which sensors each instrument supports and users cannot configure unsupported sensors).
• New SensorConfig pydantic model and sensors field in every instrument config in expedition.py.
• New SensorRegistry in utils.py that maps each SensorType to its FieldSet key, Copernicus variable name, category (phys/bgc), and Parcels particle variable name(s).
  • Per-instrument parcticle classes are now built dynamically at runtime based on which sensors are active, but the fixed/mechanical variables are still hard-coded in the instrument files, e.g. cycle_phase for Argo Floats.

API change

As mentioned above, the instruments config section of the expedition YAML now has a sensors list field, where users specify which sensors are active. For example, below the CTD is configured to sample TEMPERATURE and SALINITY:

ctd_config:
  stationkeeping_time_minutes: 50
  min_depth_meter: -11
  max_depth_meter: -2000
  sensors:
    - TEMPERATURE
    - SALINITY

• If the sensors list is omitted, it default to all valid sensors for that instrument.
• By using allowlists for each instrument, it will not allow non-sensical sensor combinations (e.g. BGC sensors on an ADCP).
• Will also not allow an empty sensor list, at least one sensor must be active.

Additional change

• Argo Float sampling kernels have been separated from the vertical-movement kernel, making it easier to add BGC sensors in a future PR.

Follow-up PRs

• The plan CLI tool will need updating to account for sensor configuration options. Currently not broken but doesn't give option to configure sensors. (New issue to be opened)
• Docs update to clearly communicate which sensors each instrument accepts, and how to configure them in either the plan tool or the expedition YAML. (New issue to be opened)
• Merge CTD + CTD_BGC into a single instrument. (Unify CTD and CTD_BGC to one instrument #260)
• Add BGC sampling to Argo Floats (New ARGO_BGC instrument #234)

Tests

• Update existing tests and add new tests to cover new sensor logic