GPS Power State tidy-up (#4161)

* Refactor GPSPowerState enum
Identifies a case where the GPS hardware is awake, but an update is not yet desired

* Change terminology

* Clear old lock-time prediction on triple press

* Use exponential smoothing to predict lock time

* Rename averageLockTime to predictedLockTime

* Attempt: Send PMREQ with duration 0 on MCU deep-sleep

* Attempt 2: Send PMREQ with duration 0 on MCU deep-sleep

* Revert "Attempt 2: Send PMREQ with duration 0 on MCU deep-sleep"

This reverts commit 8b697cd2a4.

* Revert "Attempt: Send PMREQ with duration 0 on MCU deep-sleep"

This reverts commit 9d29ec7603.

* Remove unused notifyGPSSleep Observable
Handled with notifyDeepSleep, and enable() / disable()

* WIP: simplify GPS power management
An initial attempt only.

* Honor #3e9e0fd

* No-op when moving between GPS_IDLE and GPS_ACTIVE

* Ensure U-blox GPS is awake to receive indefinite sleep command

* Longer pause when waking U-blox to send sleep command

* Actually implement soft and hard sleep..

* Dynamically estimate the threshold for GPS_HARDSLEEP

* Fallback to GPS_HARDSLEEP, if GPS_SOFTSLEEP unsupported

* Move "excessive search time" behavior to scheduler class

* Minor logging adjustments

* Promote log to warning

* Gratuitous buffer clearing on boot

* Fix inverted standby pin logic
Specifically the standby pin for L76B, L76K and clones
Discovered during T-Echo testing: totally broken function, probe method failing.

* Remove redundant pin init
Now handled by setPowerState

* Replace max() with if statements
Avoid those platform specific implementations..

* Trunk formatting
New round of settings.json changes keep catching me out, have to remember to re-enable my "clang-format" for windows workaround.

* Remove some asserts from setPowerState
Original aim was to prevent sending a 0 second PMREQ to U-blox hardware as part of a timed sleep (GPS_HARDSLEEP, GPS_SOFTSLEEP). I'm not sure this is super important, and it feels tidier to just allow the 0 second sleeptime here, rather than fudge the sleeptime further up.

* Fix an error determining whether GPS_SOFTSLEEP is supported

* Clarify a log entry

* Set PIN_STANDBY for MCU deep-sleep
Required to reach TTGO's advertised 0.25mA sleep current for T-Echo. Without this change: ~6mA.

src/sleep.h

@@ -41,8 +41,6 @@ extern Observable<void *> notifySleep;
 /// Called to tell observers we are now entering (deep) sleep and you should prepare.  Must return 0
 extern Observable<void *> notifyDeepSleep;
 
-/// Called to tell GPS thread to enter deep sleep independently of LoRa/MCU sleep, prior to full poweroff. Must return 0
-extern Observable<void *> notifyGPSSleep;
 void enableModemSleep();
 #ifdef ARCH_ESP32
 void enableLoraInterrupt();