Support recipe v1 in Build2HostMigrator

[mgorny]

Description:

Add support for v1 recipes in Build2HostMigrator, and extend the relevant tests. I've also replaced the explicit schema version check with a super() call.

Checklist:

• Pydantic model updated or no update needed

Cross-refs, links to issues, etc:

From the list on #3642

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 76.29%. Comparing base (c58f988) to head (54dfe9f).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
conda_forge_tick/migrators/cross_compile.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3808      +/-   ##
==========================================
- Coverage   77.73%   76.29%   -1.45%     
==========================================
  Files         136      136              
  Lines       14779    14787       +8     
==========================================
- Hits        11489    11282     -207     
- Misses       3290     3505     +215     

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[beckermr]

A few things but otherwise looks great! Thank you!

[isuruf]

These migrators are for easy transition from conda-build 2 to 3. I think we should drop this mini-migrator.

[mgorny]

Well, either way is fine with me. I've figured out it makes sense to keep it, in case people conda-recipe-manager convert an old recipe to v1. Technically, I suppose with v1 we could rewrite it to use ruamel.yaml, but I don't think there's a point in spending that much effort on it.

[beckermr]

I agree it can be dropped. For that, we need to remove it from the various bits of the make_migrators file. Once we do that we can merge.

Changes have been addressed.