update Pex to 2.57.0

[cburroughs]

Changelogs:

• https://github.com/pex-tool/pex/releases/tag/v2.56.0
• https://github.com/pex-tool/pex/releases/tag/v2.57.0

Lockfile diff: 3rdparty/python/user_reqs.lock [python-default]

==                    Upgraded dependencies                     ==

  cryptography                   45.0.7       -->   46.0.1
  pex                            2.55.2       -->   2.57.0
  pydantic                       1.10.22      -->   1.10.23
  pynacl                         1.5.0        -->   1.6.0

[jsirois]

The Pex 2.58.0 release is out and completes the repo --source work started in Pex 2.56.0 and improved in Pex 2.57.0. Depending on whether or not Pants options / requirements file handling get in the way, the trio of features should allow the following issues to be closed with little to no work on Pants part:

• Improve PyTorch support #18293
• Improved workflows for Torch (and Tensorflow?) #18965
• [v2.20.0] Lockfile generation with multiple indexes fails due to mismatching hashes #20808
• Respect -i/--index flags in requirements files when generating lockfiles #22581