Pex

This release brings a fix for leaks of Pex's vendored `attrs` onto the
`sys.path` of PEXes during boot in common usage scenarios.

* Fix vendored attrs `sys.path` leak. (2328)

This release adds support for tab completion to all PEX repls running
under Pythons with the `readline` module available. This tab completion
support is on-par with newer Python REPL out of the box tab completion
support.

* Add tab-completion support to PEX repls. (2321)

This release fixes a bug in `pex3 lock update` for updates that leave
projects unchanged whose primary artifact is an sdist.

* Fix lock updates for locks with sdist bystanders. (2325)

This release optimizes wheel install overhead for warm caches. Notably,
this speeds up warm boot for PEXes containing large distributions like
PyTorch as well as creating venvs from them.

* Lower noop wheel install overhead. (2315)

This release brings support for `--pip-version 23.3.2` along with
optimizations that reduce built PEX size for both `--include-tools` and
`--venv` PEXes (which includes the Pex PEX) as well as reduce PEX build
time for `--pre-install-wheels` PEXes (the default) and PEX cold first
boot time for `--no-pre-install-wheels` PEXes that use more than one
parallel install job.

* Add support for Pip 23.3.2. (2307)
* Remove `Pip.spawn_install_wheel` & optimize. (2305)
* Since we no longer use wheel code, remove it. (2302)

This release brings three new features:

1. When creating PEXes without specifying an explicit
`--python-shebang`, an appropriate shebang is chosen correctly in
more cases than previously and a warning is emitted when the shebang
chosen cannot be guaranteed to be correct. The common case this
helps select the appropriate shebang for is PEXes built using
`--platform` or `--complete-platform`.
2. PEXes can now be created with `--no-pre-install-wheels` to cut down
PEX build times with a tradeoff of roughly 10% greater boot overhead
upon the 1st execution of the PEX file. For PEXes with very large
dependency sets (machine learning provides common cases), the build
time savings can be dramatic.
3. PEXes can now be told to install dependencies at runtime on 1st
execution using parallel processes using `--max-install-jobs` at PEX
build time or by setting the `PEX_MAX_INSTALL_JOBS` environment
variable at runtime.

The last two features come with complicated tradeoffs and are turned off
by default as a result. If you think they might help some of your use
cases, there is more detail in the command line help for
`--no-pre-install-wheels` and `--max-install-jobs` as well as in the
`pex --help-variables` output for `PEX_MAX_INSTALL_JOBS`. You can also
find a detailed performance analysis in 2292 for the extreme cases of
very small and very large PEXes. In the end though, experimenting is
probably your best bet.

* Use appropriate shebang for multi-platform PEXes. (2296)
* Add support for --no-pre-install-wheels and --max-install-jobs. (2298)