Pex

This release adds support for injecting requirements into the isolated
Pip PEXes Pex uses to resolve distributions. The motivating use case
for this is to use the feature Pip 23.1 introduced for forcing
`--keyring-provider import`.

Pex already supported using a combination of the following to force
non-interactive use of the keyring:
1. A `keyring` script installation that was on the `PATH`
2. A `--pip-version` 23.1 or newer.
3. Specifying `--use-pip-config` to pass `--keyring-provider subprocess`
to Pip.

You could not force `--keyring-provider import` though, since the Pips
Pex uses are themselves hermetic PEXes without access to extra
installed keyring requirements elsewhere on the system. With
`--extra-pip-requirement` you can now do this with the primary benefit
over `--keyring-provider subprocess` being that you do not need to add
the username to index URLs. This is ultimately because the keyring CLI
requires username whereas the API does not; but see
https://pip.pypa.io/en/stable/topics/authentication/#keyring-support for
more information.

* Add support for `--extra-pip-requirement`. (2461)

This release adds support for Pip 24.1.2.

* Add support for `--pip-version 24.1.2`. (2459)

This release fixes the `bdist_pex` distutils command to use the
`--project` option introduced by 2455 in the 2.8.0 release. This
change produces the same results for existing invocations of
`python setup.py bdist_pex` but allows new uses passing locked project
requirements (either hashed requirement files or Pex lock files) via
`--pex-args`.

* Fix `bdist_pex` to use `--project`. (2457)

This release adds a new `--override` option to resolves that ultimately
use an `--index` or `--find-links`. This allows you to override
transitive dependencies when you have determined they are too narrow and
that expanding their range is safe to do. The new `--override`s and the
existing `--exclude`s can now also be specified when creating or syncing
a lock file to seal these dependency modifications into the lock.

This release also adds a new `--project` option to `pex` and
`pex3 lock {create,sync}` that improves the ergonomics of locking a
local Python project and then creating PEX executables for that project
using its locked requirements.

In addition, this release fixes the `bdist_pex` distutils command that
ships with Pex to work when run under `tox` and Python 3.12 by improving
Pex venv creation robustness when creating venvs that include Pip.

* Add support for `--override`. (2431)
* Support `--project` locking and PEX building. (2455)
* Improve venv creation robustness when adding Pip. (2454)

This release adds support for Pip 24.1.1.

* Add support for `--pip-version 24.1.1`. (2451)

There are no changes to Pex code or released artifacts over 2.6.1 or