compare sketch parameter parsing, generation with sourmash python layer strategies + testing

[bluegenes]

Now that the buildutils.rs file contains ~standardized utilities for sketch building, it would be useful to look back at the sourmash python layer parameter string parsing + sketching to compare strategies and make sure we're not missing anything. The goal is to standardize on good behavior we can add to sourmash core.

1. param string parsing:

• here, MRG: validate param strings #114 introduced validation of sketching parameter strings and rust-level testing
• compare with: sourmash python parsing code; test file.

2. template sketch building:

• here: BuildCollection (and associated BuildManifest) holds the template sketches and has methods to populate with sequence.
• in sourmash it is: signatures_for_sketch_factory.

I think sketch_factory may have some better handling of protein vs dna defaults, here we only have a single default set of parameters at the rust level (dna,k=31,scaled=1000)

also related: #113