refactor(hts221): Verify equivalence with WSEN-HIDS and drop HTS221 driver

[nedseb]

Context

The STeaMi board ships a Würth WSEN-HIDS (P/N 2525020210001), not an ST HTS221. The wiki confirms this — docs/hardware/main-components/sensors/wsen-hids.md declares WSEN-HIDS as the installed humidity + temperature sensor.

Both drivers currently live in this repo:

• lib/hts221/ (238 lines in device.py) — minimal, legacy
• lib/wsen-hids/ (404 lines in device.py) — current, with averaging support, custom exceptions, two-point calibration

Register-level comparison (lib/hts221/hts221/const.py vs lib/wsen-hids/wsen_hids/const.py):

Field	hts221	wsen-hids
I2C address	0x5F	0x5F
Device ID	0xBC (WHO_AM_I)	0xBC
Register map	identical	identical (more exposed)
ODR encodings	identical	identical
Calibration	factory only	factory + 2-point user
Averaging	not exposed	AVG_2…AVG_256 constants

WSEN-HIDS is a second-source of HTS221 — same silicon family, fully drop-in. Keeping both modules is dead weight against real STeaMi hardware and confuses users.

Scope

Phase 1 — Confirm equivalence

• Diff hts221/const.py and wsen_hids/const.py register-by-register.
• Diff hts221/device.py and wsen_hids/device.py method-by-method.
• Cross-check on real hardware that wsen_hids returns plausible values on the STeaMi internal I2C bus.
• List any HTS221-only feature that is not present in WSEN-HIDS — port it over before removal. (Expected: none. WSEN-HIDS is a strict superset.)

Phase 2 — Remove lib/hts221

• Delete lib/hts221/ (driver, examples, README, manifest, tests).
• Remove HTS221 entries from the README driver table and any aggregated docs.
• Audit tests/ scenarios for hts221 references — retarget temperature/humidity comparison scenarios onto wsen_hids where applicable.
• Sweep manifest.py / package metadata for hts221 entries.

Out of scope

• Custom boards mounting a real ST HTS221 — the WSEN-HIDS driver works on them too (identical silicon-level behavior).

Cross-repo

Mirror issues are being filed on arduino-steami-lib (same duplication) and wiki_steami (residual HTS221 mention in docs/design/sensors.md).