Override resource location for a particular package installed through `pip install -r requirements.txt`

Hi,

We have numpy pinned in `requirements.txt`. Is there a way to override the resource location for `numpy` specifically without duplicating the numpy install in pyoxidizer.bzl using `exe.pip_download`?

Start by tracing how requirements.txt is processed and how exe.pip_download handles package resource locations in pyoxidizer.bzl. Determine whether a per-package override can be represented without duplicating numpy installation, then verify that a requirements-based install still uses the requested location for numpy.

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