[WIP] gh-107954: Add _PyConfig_Parse()

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• Issue: [C API] PEP 741: Add PyInitConfig C API to customize the Python initialization #107954

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Discussion: https://discuss.python.org/t/fr-allow-private-runtime-config-to-enable-extending-without-breaking-the-pyconfig-abi/18004

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It may be interesting to store unknown variables in a dictionary and expose it somewhere, similar to sys._xoptions. It would allow implement https://discuss.python.org/t/fr-allow-private-runtime-config-to-enable-extending-without-breaking-the-pyconfig-abi/18004 use case: private vendor-specific variables.

For that, the configuration format should have a deterministic way to get the type of unknown variable. In sys._xoptions, the key is a string and the value is a string or True if there is no value.

Looking at TOML specification, I see the following types would be interesting to support:

• boolean
• integer
• string
• array of string

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I abandon this approach based on text configuration: see https://discuss.python.org/t/fr-allow-private-runtime-config-to-enable-extending-without-breaking-the-pyconfig-abi/18004/24 for the rationale.

Let's focus on PR #110176 PyInitConfig API instead which seem to be please more people.