drivers: Ensure read methods auto-trigger conversion in power-down mode.

[nedseb]

Problem

Some drivers do not automatically trigger a conversion when measurement methods are called while the sensor is in power-off or idle mode.

Convention

When a driver is powered off or idle, calling any measurement method should automatically trigger a conversion before reading. All drivers implement _ensure_data() which checks the power state and triggers a conversion if needed, with polling and timeout (OSError on failure).

Reference pattern: _ensure_data() (see WSEN-PADS, WSEN-HIDS, HTS221).

Audit results

Fixed

• WSEN-PADS (PR wsen-pads: Add pressure sensor driver. #3): _ensure_data() triggers one-shot, polls STATUS_P_DA | STATUS_T_DA, raises WSENPADSTimeout
• WSEN-HIDS: _ensure_data() triggers one-shot, polls data_ready(), raises WSENHIDSTimeoutError
• HTS221 — hts221: Auto-trigger one-shot conversion in power-down mode. #69 — PR hts221: Auto-trigger one-shot conversion in power-down mode. #68: _ensure_data() triggers one-shot, polls STATUS_T_DA | STATUS_H_DA, raises OSError
• LIS2MDL — lis2mdl: Auto-trigger single conversion in idle mode. #70 — PR lis2mdl: Auto-trigger single conversion in idle mode. #73: _ensure_data() triggers single conversion, polls data_ready(), raises OSError
• VL53L1X — vl53l1x: Check data ready and clear interrupt in read(). #71 — PR vl53l1x: Check data ready and clear interrupt in read(). #74: _ensure_data() starts ranging, polls data_ready(), clears interrupt, raises OSError
• APDS9960 — apds9960: Auto-enable sensor when reading without active mode. #72 — PR apds9960: Auto-enable sensor when reading without active mode. #75: _ensure_light_enabled() / _ensure_proximity_enabled() auto-enable sensor, poll readiness, raise OSError
• ISM330DL — ism330dl: Ensure read methods auto-trigger conversion in power-down mode. #123 — PR ism330dl: Auto-trigger conversion when reading after power down. #124: _ensure_data() restores ODR, polls all status bits, raises OSError

To audit

• BME280 — driver not yet written (bme280: Add two-point temperature calibration methods. #108)
  Auto-trigger behavior to be verified once driver is implemented

Not concerned

• BQ27441: battery gauge, always active — no power-off mode
• MCP23009E: GPIO expander — no conversion concept
• SSD1327: display driver — no conversion concept

[nedseb]

Updated sub-issues tracker

Driver	Status	Issue	PR
wsen-pads	Done	—	PR #3
wsen-hids	Done	—	—
hts221	Done	#69	PR #68 (merged)
lis2mdl	Draft	#70	PR #73 (draft)
vl53l1x	Draft	#71	PR #74 (draft)
apds9960	Draft	#72	PR #75 (draft)
ism330dl	To audit	—	PR #50 (in review)

Not concerned: bq27441, mcp23009e, ssd1327.