Freeze when writing files from Bluetooth HCI event handler

[Slion]

After integrating raspberrypi/pico-sdk#1715 I'm getting a crash when writing files from Bluetooth HCI event handler.
File system is configured with LittleFS from flash on a Pico W.
I'm attempting to replace my own custom flash storage which worked fine from the Bluetooth HCI event handler.
Tried to use save_and_disable_interrupts but that did not help.
Not sure what's going on exactly is it a deadlock somehow or is it a crash.

Writing to files from main or the Bluetooth timer callback works fine it seems.

Switching the btstack configuration from background to poll changes the context in which the Bluetooth HCI handler is run from IRQ to thread. When running from the thread writing to files works fine.

It also shows that not all IRQs are equals. The btstack timer IRQ could write to files but the HCI IRQ could not.

[Slion]

Even with background async context and running HCI callbacks from the thread rather than ISR I could still get freeze especially when creating files. I'm guessing it would stall btstack and it does not like that.

I have to take all files operation out of the HCI callbacks.
That's not an issue with pico-vfs itself.