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/variant.cpp

@@ -67,9 +67,11 @@ void initVariant() {
     pinMode(PIN_QSPI_CS, OUTPUT);
     digitalWrite(PIN_QSPI_CS, HIGH);
 
-    // VBAT_ENABLE: keep LOW by default, WioTrackerL1Board::getBattMilliVolts() toggles it
+    // VBAT_ENABLE: hold HIGH so the battery voltage divider is always on and its
+    // node stays settled for the ADC read (getBattMilliVolts). Per-read gating
+    // left it unsettled at sample time -> high/jittery readings.
     pinMode(VBAT_ENABLE, OUTPUT);
-    digitalWrite(VBAT_ENABLE, LOW);
+    digitalWrite(VBAT_ENABLE, HIGH);
 
     // set LED pin as output and set it low
     pinMode(PIN_LED, OUTPUT);