MinHash compatibility check to sourmash sig intersect

[erikyoung85]

This PR calls minhash.is_compatible(...) to check for MinHash compatibility before intersecting two MinHashes.
Fixes #1107

• 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 #1116 into master will increase coverage by 8.80%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1116      +/-   ##
==========================================
+ Coverage   83.84%   92.64%   +8.80%     
==========================================
  Files          98       74      -24     
  Lines        9111     5792    -3319     
==========================================
- Hits         7639     5366    -2273     
+ Misses       1472      426    -1046     

Flag	Coverage Δ
#rusttests	?

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Impacted Files	Coverage Δ
sourmash/sig/__main__.py	93.34% <100.00%> (-0.06%)	⬇️
sourmash/_compat.py	52.17% <0.00%> (-47.83%)	⬇️
sourmash/signature.py	90.82% <0.00%> (-2.30%)	⬇️
sourmash/lca/lca_utils.py	91.20% <0.00%> (-1.60%)	⬇️
sourmash/lca/command_index.py	92.70% <0.00%> (-0.53%)	⬇️
sourmash/sbt.py	88.57% <0.00%> (-0.28%)	⬇️
src/core/src/index/mod.rs
src/core/src/ffi/nodegraph.rs
src/core/src/ffi/cmd/compute.rs
src/core/src/index/storage.rs
... and 22 more

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[ctb]

hmm, well, as long as we're here... per #1107 (comment), is_compatible returns a bool. Could you change the try/except here and in subtract to test is_compatible(...) and complaining, rather than catching an exception? thx!

[ctb]

sorry, I misled you - instead of raising ValueError, can you do the error(...) and sys.exit(-1)? These are direct command line calls so it makes more sense for the user to see some error text than a raised exception, since non-Python programmers may be running these.

[erikyoung85]

Oh definitely! Thats good to know, I was wondering about the difference between the two because I've seen both in the code.

[ctb]

thank you!