Python install manager 26.4

Along with Python 3.15.0rc2, the second beta of the next Python install manager release is also available. The changes in beta 1 are more interesting (though I forgot to post about them), but the two main changes are that ARM64 machines will now default to the ARM64 platform (that is, py -3.15 is equivalent to py -3.15-arm64 on an Arm device), and support has been added for HTTP_PROXY, HTTPS_PROXY and NO_PROXY environment variables. Previously, the OS-wide proxy settings and authentication w...