fix: SPI transactions on esp32

[rpocklin]

Summary
This is an issue I was facing using this sensor on ESP32 and was recently raised by another person also: (#19)

On platforms where beginTransaction() acquires a mutex (e.g. ESP32), failing to call endTransaction() causes the second SPI call to deadlock.

IO_Read and IO_Write both called beginTransaction() but never released the bus, causing the MCU to freeze during init() firmware upload.

STM32 is unaffected as beginTransaction() is a no-op (ie. this is a non-breaking aka backwards compatible change).

This PR fixes/implements the following:

• Bug / Feature - Add tested support for esp32 by ensuring endTransaction() is called when using SPI

Motivation
This library works perfectly on esp32 once this issue is fixed, without it, it hangs on the second transaction due to the mutex.

Validation
Tested with demo sketch in both PlatformIO v6.1.19 and Arduino IDE v2.3.8.

Closing issues
Closes #19

[fpistm]

Sounds good.

[cparata]

Hi @rpocklin ,
Thank you for the PR! I released a new version of the library including this fix.
Best Regards,
Carlo

[rpocklin]

Thanks, I just upgraded to it now - appreciate you merging it so quickly 🚀

You may have to do a separate publish for the new library version to reach the PlatformIO registry:
pio pkg publish