[MRG] add -A/--abundance-from to sig subtract & add sig inflate

[ctb]

This PR adds -A/--abundance-from to the sourmash sig subtract command, per #1888.

It also:

• implements implicit intersection in MinHash.inflate(...) in the situation where self is not a subset of from_mh
• adds tests for this feature of MinHash.inflate(...)
• cleans up the abundance borrowing code in sourmash sig intersect -A to use MinHash.inflate(...)
• adds sourmash sig inflate

Fixes #1888
Fixes #1706

TODO:

• add more tests for sourmash sig inflate
• add docs for sourmash sig inflate
• add a note about other places where save_signatures is being used (now in several sourmash sig commands do not use 'modern' signature output methods #1890)

[codecov]

Codecov Report

Merging #1889 (606362e) into latest (dd5c013) will increase coverage by 8.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           latest    #1889      +/-   ##
==========================================
+ Coverage   82.64%   90.65%   +8.01%     
==========================================
  Files         121       92      -29     
  Lines       13159     8998    -4161     
  Branches     1774     1780       +6     
==========================================
- Hits        10875     8157    -2718     
+ Misses       2018      577    -1441     
+ Partials      266      264       -2     

Flag	Coverage Δ
python	90.65% <100.00%> (+0.10%)	⬆️
rust	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/sourmash/cli/sig/__init__.py	100.00% <100.00%> (ø)
src/sourmash/cli/sig/inflate.py	100.00% <100.00%> (ø)
src/sourmash/cli/sig/subtract.py	100.00% <100.00%> (ø)
src/sourmash/minhash.py	92.56% <100.00%> (ø)
src/sourmash/sig/__main__.py	92.95% <100.00%> (+1.11%)	⬆️
src/core/src/ffi/signature.rs
src/core/src/errors.rs
src/core/tests/minhash.rs
src/core/src/ffi/index/revindex.rs
src/core/src/lib.rs
... and 27 more

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[ctb]

@taylorreiter thoughts and suggestions welcome! I think it's mostly done, will put it up for review if when I look at it with fresh eyes it seems good (and all the code is covered).

[taylorreiter]

ooooh sig inflate is really cool. The documentation is nice a clear too! I don't really have any suggestions, I think the clear documentation is the biggest key, as with that I think I can imagine different ways to get what I want using combinations of the sourmash sig commands. This is awesome!

[ctb]

ok, this is now ready for review and merge @sourmash-bio/devs! No particular hurry.