Add ios_ver and _multiarch shims for pip 24.3 support.

[freakboy3742]

Pip 24.3 includes explicit support for iOS as a platform; the sitecustomize shim provided by the support package triggers this handling. However, it then requires platform.ios_ver() and sys.implementation._multiarch to return the correct values to determine the tag name.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct