Exercise the debug structs placed in PyRuntime

[pablogsal]

To avoid breaking external inspection, profilers and debuggers too often or to make supporting them too difficult, we added a special offset struct in the PyRuntime structure. Unfortunately there is nothing testing that this offsets are correct or that they are enough to analyse or profile a Python application on their own. To fix this, we should add some testing that exercises the offsets and ensure they are enough to serve the purpose they were added.

Linked PRs

• gh-115773: Add tests to exercise the _Py_DebugOffsets structure #115774
• gh-115773: Add missing preprocessor guard in _testexternalinspection #116212
• gh-115773: Use the right variable name based on the field we are trying read #118591
• gh-115773: Add sizes to debug offset structure #120112
• [3.13] gh-115773: Add sizes to debug offset structure (GH-120112) #121283