add SPI driver for semtech sx128x chips (#864)

* add SPI driver for semtech sx128x chips

Co-authored-by: Copilot <copilot@github.com>

* handle busy loop better

* switch to time based busy timeout

Co-authored-by: Copilot <copilot@github.com>

* comment functions

* start on using types for function inputs

* use types where applicable and align with datasheet more

Co-authored-by: Copilot <copilot@github.com>

* work on exporting less constants

* only export "actionable" errors

* combine identical constants

* add crude lora rx and tx examples

* change from type aliases to local types

---------

Co-authored-by: Copilot <copilot@github.com>

sx128x/errors.go

@@ -0,0 +1,19 @@
+package sx128x
+
+import "errors"
+
+var (
+	ErrBusyPinTimeout        = errors.New("busy pin timeout")
+	errDataTooLong           = errors.New("data over 256 bytes")
+	errInvalidSleepConfig    = errors.New("invalid sleep config")
+	errInvalidStandbyConfig  = errors.New("invalid standby config")
+	errFrequencyTooLow       = errors.New("frequency below 2.4Ghz")
+	errFrequencyTooHigh      = errors.New("frequency above 2.5Ghz")
+	errPowerTooLow           = errors.New("power level below -18dBm")
+	errPowerTooHigh          = errors.New("power level above 13dBm")
+	errInvalidPeriodBase     = errors.New("invalid period base")
+	errInvalidPacketType     = errors.New("invalid packet type")
+	errInvalidRegulatorMode  = errors.New("invalid regulator mode")
+	errPayloadLengthTooShort = errors.New("payload length too short")
+	errPayloadLengthTooLong  = errors.New("payload length too long")
+)