feat: add support for md5 hash in direct url requests and add it to cache key

[wolfv]

This would help a lot when installing explicit environments, because they usually come with md5 hashes (from the old days...).

The environments look something like this:

# This file may be used to create an environment using:
# $ conda create --name <env> --file <this file>
# platform: osx-arm64
@EXPLICIT
https://conda.anaconda.org/conda-forge/osx-arm64/libcxx-20.1.1-ha82da77_0.conda#833c4899914bf96caf64b52ef415e319
https://conda.anaconda.org/conda-forge/osx-arm64/micromamba-1.5.12-0.tar.bz2#ef854aa57525cb8d9a87cc1f1d59bd92

From which we can construct matchspecs like:

libcxx[url="https://conda.anaconda.org/conda-forge/osx-arm64/libcxx-20.1.1-ha82da77_0.conda", md5="833c4899914bf96caf64b52ef415e319"]

Which rattler / py-rattler would then install perfectly fine.

cc @johanneskoester

[baszalmstra]

Did you also change writing the md5 to the cache lock file?

[wolfv]

That should happen since I add it to the CacheKey and we use the information from RepodataRecord if present (i think we fill it in if not present, when downloading).

[wolfv]

superseded by #1293