feat: Reed-Solomon decoder accept FFT domain

[ggutoski]

Description

close: #261

• Builds upon Refactor Reed Solomon code #256. Merge target is rs-code-fft instead of main so you can see the stuff I added to Refactor Reed Solomon code #256. If desired we could change the merge target to main and close Refactor Reed Solomon code #256.
• New function reed_solomon_erasure_decode_rou accepts FFT domain and wraps reed_solomon_erasure_decode.
• House cleaning: change reed_solomon_erasure_encode into an iterator adaptor. (ie. It now returns an iterator.) It's not obvious/easy to do the same for reed_solomon_erasure_decode so I didn't do that.

Warning

(UPDATE: fixed in 08e870f . See #309 (comment) . )

Naive implementation of reed_solomon_erasure_decode_rou computes each eval point in linear time. Ideally we would like constant-time random access to domain points without allocating and populating a vec for all the points. How best to achieve that?

jellyfish/primitives/src/reed_solomon_code/mod.rs

Lines 157 to 158 in 8baf5e0

	// TODO(Gus) nth runtime is linear in index!
	(domain.elements().nth(index).unwrap(), eval)

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[mrain]

Generally LGTM. I think we can close the previous PR and directly merge this one to the main branch.

[mrain]

LGTM!