fix(oss): Get integration tests running

[ben--]

Recent changes to EdenFS have caused the OSS build of integration tests to go stale. These are some targeted fixes to get them working again:

1. Make the python-psutil package available
2. Fix the build "egg" generation

The second one puts a wrap on all the changes required by recent updates to EdenFS that required hybrid (python+native and/or cython) libraries.

The weirdest part that was required was renaming the targets to end in .egg -- this is actually required by one part of the python build infrastructure which tries to detect whether it is in a directory that ends with the .egg extension.

Tested through building Sapling/EdenFS (requires other fixes to run clean):

act --container-architecture linux/x86_64 -W .github/workflows/edenfs_linux.yml

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