Audit flexspi HAL for panics

[kurtjd]

Removes unwraps and most indexing/slicing (two cases of slicing were left in but are very easy to see they can never panic) from the flexspi HAL.

I use this pattern several times for copying a remainder (which may be less than a 4 byte chunk):

for (to, from) in remainder.iter_mut().zip(data.to_le_bytes().iter()) {
    *to = *from;
}

since it avoids the need to use copy_from_slice (with a calculated min length). However, this may be slightly less efficient than the equivalent copy_from_slice especially since the compiler should be able to elide the panic path as remainder size can be determined statically (as_chunks::<N> guarantees statically that remainder length is less than N). Open to using the slice method with an allow lint if folks prefer.

Testing

The changes in peripheral.rs I was able to test by copying the unit tests to another project with my new implementations and verifying they pass (speaking of, I can't figure out how to get cargo test to work here).

My other changes I at least tested using the flexspi-embedded-storage and flexspi-nor-flash examples on the 685evk. Still having issues getting the flexspi-nor-flash example working properly as I'm having trouble receiving defmt logs to verify it's functioning correctly.

Resolves OpenDevicePartnership/embedded-services#643

[jerrysxie]

@kurtjd flexspi-storage-service example is not working? I believe it requires loading the image into RAM. You can look at how to do it from this PR: #336.

[kurtjd]

@kurtjd flexspi-storage-service example is not working? I believe it requires loading the image into RAM. You look at how to do it from this PR: #336.

Ah thanks, I will give that a try.

[jerrysxie]

Can you add a testing section to the PR description to indicate which flash example was ran with this change?

[jerrysxie]

Can you add a testing section to the PR description to indicate which flash example was ran with this change?

Oh, and please announce the breaking change on Zulip, once it is ready to be merged.

[kurtjd]

Can you add a testing section to the PR description to indicate which flash example was ran with this change?

Oh, and please announce the breaking change on Zulip, once it is ready to be merged.

Done.

[bramsdell-ms]

Maybe:

let data_bytes = cmd.data_bytes.ok_or(NorStorageBusError::StorageBusInternalError)?

[kurtjd]

Ah yeah that is cleaner, unfortunately already merged :(