fix: don't uninstall PyPI files that a conda package now owns

[baszalmstra]

Description

Moving a PyPI dependency to the conda side leaves the package half-deleted: the .py files are gone but some data files survive.

When that was the last PyPI dependency of the environment, on_python_interpreter_change sees an empty set of PyPI records and cleans out site-packages. The old PyPI .dist-info is still sitting there, and its RECORD lists exactly the paths the conda package just wrote, so we uninstall the freshly installed conda files. Only the files that differ between the two versions survive, which matches the symptoms in the issue.

Before uninstalling a distribution we now look up its RECORD entries in the conda paths registry we already build for the clobber warnings. If a conda package owns any of them, only the stale .dist-info is removed and the files are left alone. The registry is built after we know there is something to uninstall, so the common "environment has no PyPI dependencies" path does not pay for it on every run (~15 ms on a 109-package env).

Entries of an installed distribution need slightly different handling than a wheel RECORD: they are relative to the directory holding the .dist-info and the PEP 427 .data/<scheme>/... entries have already been spread out by the installer. Hence from_installed_record next to from_wheel_record.

Fixes #6902

How Has This Been Tested?

cargo test -p pixi_install_pypi, with three new unit tests for mapping installed-RECORD entries onto conda's prefix-relative form: a plain entry, a ../../../bin/<script> console script that escapes site-packages but stays inside the prefix, and entries that escape the prefix or are absolute.

I did not manage to build an integration test for the full move-to-conda flow, so that path is reasoned about rather than verified. Please check it closely.

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Tools: Claude

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added sufficient tests to cover my changes.