IllegalInstruction exception when using embassy

[TheButlah]

Looks like the atomic trap handler in esp-hal is being a ඞඞsussy bakaඞඞ

Blocked by esp-rs/riscv-atomic-emulation-trap#3 and also knurling-rs/defmt#597
Related: embassy-rs/embassy#995

Options for workarounds:

• proceed as normal (i.e. compile to -imac and use trap handler) but compile just embassy with opt-level = 0
• Switch to -imc and fork defmt-rtt to use atomic-polyfill instead of core::sync::atomic

Regardless of which approach to use, I think that I should be eschewing core::sync::atomic in favor of atomic-polyfill in my code, to avoid this issue on any platforms without an atomic trap handler

I've been tracking my time spent debugging this (just for science) and I think I've spent about 24hrs over the last 4 days or so

[TheButlah]

Switching to -imc should be preferred due to the performance implications of the atomic trap, and will have support in defmt-rtt when knurling-rs/defmt#702 is merged.

The bug in the atomic trap handler has been fixed due to esp-rs/esp-hal#207 and esp-rs/riscv-atomic-emulation-trap#4. This should be live with an upcoming release of esp-hal. They mentioned it would take some small changes to esp-wifi too though, and wifi is the next thing for me to test. So I may stay on 0.2 for just a bit longer till 0.3 is published and I confirm from them on matrix that esp-wifi should work

Next steps:

1. Test that those linked PRs actually fix the issue, and let the maintainers in esp-rs know
2. Adopt the -imc approach due to performance and portability, refactor my code to no longer rely on core::sync::atomic. atomic-polyfill should be used if I feel like I need atomics.