Feat: Support restricting package installation by datetime upper bound

[notatallshaw]

Since PEP 700 simple index index API 1.1 and above has supported the field upload-time. It would be useful for many use cases to support restricting what packages are installed by specifying an upper limit on this upload-time.

Particularly because:

1. Libraries are strongly discouraged from providing upper bounds
2. Metadata can not be changed once uploaded to PyPI
3. Leading to the problem: If library A depends on library B and B releases a version that is incompatible with A, then a new version of A can get released that excludes the incompatible version of B, but this can mean that package installer might just backtrack on A and install functionality incompatible versions of A and B even though their metadata doesn't describe it

Therefore installing older requirements can sometimes be significantly helped by adding an upper limit on upload-time.

[wolfv]

Is this also how the pypi timemachine works? Would definitely be a cool feature! (https://pypi.org/project/pypi-timemachine/)

[notatallshaw]

No, pypi timemachine was created before and hasn't been updated since PEP 700.

It uses the PyPI JSON API, which is a non-standard API: https://warehouse.pypa.io/api-reference/json.html. e.g. https://pypi.org/pypi/requests/json