[MRG] Bunch of Rust refactors

[luizirber]

(These were in 6 or 7 different branches here, so I'm making a grab bag)

• Migrate from failure (deprecated) to thiserror
  • Still keep failure around for now, until the .backtrace() support is available. This is useful when debugging FFI.
• Cache md5sum calculation, which is a huge performance improvement for gather and search
• remove serde_derive and use the derive feature in serde (small paper cut)
• Use the nohash-hasher crate instead of the copy-pasted NoHashHasher from finch.
• Expose a bit more of the API for wasm (signature and ComputeParameters).
• Bump typed-builder (now that MSRV is 1.37)
• Add getters and setters for ComputeParameters instead of exposing struct.

TODO

• actually write a wasm test

Checklist

• Is it mergeable?
• make test Did it pass the tests?
• make coverage Is the new code covered?
• Did it change the command-line interface? Only additions are allowed
  without a major version increment. Changing file formats also requires a
  major version number increment.
• Was a spellchecker run on the source code and documentation after
  changes were made?

[codecov]

Codecov Report

Merging #1058 into master will increase coverage by 9.34%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1058      +/-   ##
==========================================
+ Coverage   83.94%   93.29%   +9.34%     
==========================================
  Files          99       74      -25     
  Lines        9065     5963    -3102     
==========================================
- Hits         7610     5563    -2047     
+ Misses       1455      400    -1055     

Flag	Coverage Δ
#rusttests	?

Impacted Files	Coverage Δ
sourmash/sourmash_args.py	95.27% <0.00%> (-0.30%)	⬇️
sourmash/cli/sig/cat.py	100.00% <0.00%> (ø)
src/core/src/from.rs
src/core/src/ffi/mod.rs
src/core/tests/test.rs
src/core/src/ffi/minhash.rs
src/core/src/index/search.rs
src/core/src/ffi/nodegraph.rs
sourmash/sig/__main__.py	96.54% <0.00%> (+3.28%)	⬆️

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[luizirber]

Ready for review and merge @ctb

[ctb]

Nothing in the Python code or UX was changed, and I did a light skim of the Rust code 👍