"Prefilter Shard Records on Python Minor Version"

[dholth]

Checklist

• I added a descriptive title
• I searched open requests and couldn't find a duplicate

What is the idea?

mamba-org/mamba@8c09112 is mamba's implementation of mamba-org/mamba#4214.

They take advantage of the fact that Python is pinned in users' environments to discard shards in the shard traversal phase; then retry if that doesn't work.

Why is this needed?

Improve performance of sharded repodata.