DISCO_L072CZ_LRWAN1 LOW POWER

This is a follow-on from #119 which never seems to have adequately resolved.

In addition to getting ~300uA on VDD_MCU when the event loop is idle, I always see ~1mA on VDD_USB. I believe this is due to TCXO being powered by PA_12 (with JP9 in position 1-2) and this always staying high in the SX1276 library. If JP9 is in position 2-3 then the 1mA shifts to VDD_LRA (since this hard-wires TCXO to always on).

So problem 1 is how to control PA_12/TCXO so it is off when the event loop is idle. This could be done manually by setting sx1276-lora-driver.tcxo to NC and manually turning it on before a send and off following a send but this seems a bit hacky.

And problem 2 is how to further reduce MCU consumption in deep sleep.

Both of these are crucial for a battery powered IoT application which is the target of this library.

Start by comparing this report with follow-on issue #119 and inspect the SX1276 library's handling of PA_12/TCXO during an idle event loop, including the suggested tcxo setting. Measure VDD_MCU and VDD_USB in idle and deep sleep, then confirm completion when TCXO is disabled while idle and MCU consumption is reduced without disrupting sends.

Written by the indexing model from the issue text.