fix(wio-tracker-l1): battery voltage reads high/jittery — divider always on

The per-read VBAT_ENABLE gating from 4d46abb2 (energy optimizations)
powered the battery voltage divider HIGH for only 10ms before each ADC
read, then LOW. 10ms is too short for the high-impedance divider node
to settle before the nRF52 SAADC samples it, so readings came out high
and inconsistent (e.g. 4.6-5.0V on a LiPo that maxes ~4.2V).

Hold VBAT_ENABLE HIGH continuously again (as before 4d46abb2) so the
node is always settled at sample time, and drop the toggle + delay(10)
from getBattMilliVolts(). Standby cost is ~2uA on the 2x1M divider,
negligible next to the device's mA-level draw.

The CPU-sleep and LED-off energy optimizations from 4d46abb2 are left
untouched — those are the real savings; only the VBAT gating is reverted.

variants/wio-tracker-l1/WioTrackerL1Board.h

@@ -22,12 +22,12 @@ public:
 #endif
 
   uint16_t getBattMilliVolts() override {
-    digitalWrite(VBAT_ENABLE, HIGH);
+    // VBAT_ENABLE is held HIGH continuously (see begin()/initVariant()) so the
+    // divider node is already settled — don't gate it per-read, that reads high
+    // and jittery because 10ms wasn't enough for the divider to stabilize.
     analogReadResolution(12);
     analogReference(AR_INTERNAL);
-    delay(10);  // allow voltage divider to stabilize
     int adcvalue = analogRead(PIN_VBAT_READ);
-    digitalWrite(VBAT_ENABLE, LOW);
     return (adcvalue * ADC_MULTIPLIER * AREF_VOLTAGE) / 4.096;
   }