feat: Primer3 takes a list of VCFs instead of a VariantLookup object

[emmcauley]

Closes #53.

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Codecov Report

Attention: Patch coverage is 84.61538% with 2 lines in your changes missing coverage. Please review.

Project coverage is 97.26%. Comparing base (c434b1d) to head (0a83439).

Files with missing lines	Patch %	Lines
prymer/primer3/primer3.py	84.61%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #62 +/- ## ========================================== - Coverage 97.37% 97.26% -0.11% ========================================== Files 25 25 Lines 1601 1610 +9 Branches 302 303 +1 ========================================== + Hits 1559 1566 +7 - Misses 23 24 +1 - Partials 19 20 +1 ```

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[tfenne]

I'd appreciate @msto's feedback on this PR. I think original the thought was it would just be a list of VCFs vs. a VariatnLookup, but the reality of it being 4 parameters that control how variants are read from VCFs, makes it less desirable IMHO.

I think I would propose either:

• Creation of a small dataclass (e.g. VariantParams) to hold a list of VCFs and all the other parameters that effect VariantLookup creation, and then optionally take that in primer3.py? (Or VariantParams | VariantLookup | None).
• Go back to just having it take a Variant Lookup

But I'd wait for @msto's input before doing anything further.