Deprecate PyTracebackObject struct

[kumaraditya303]

See https://discuss.python.org/t/leaky-abstractions-and-cpython-performance/18392 for discussion.

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The entire struct would be deprecated under this issue. For deprecating PyTracebackObject the following changes will be performed under this issue in 3.12:

• Mark the entire struct with Py_DEPRECATED(3.12)
• Add C API function to access tb_lineno in C.
• Document the changes in What's New with fallback code snippets for older versions.

Changes in 3.14:

• The struct would be removed from the public C headers and moved to the internal C API.
• The optimizations would be implemented.

[gvanrossum]

Hold your horses. I’m not convinced yet that we should do this.

[kumaraditya303]

@gvanrossum What alternative do we have? Or do you mean this should be done at all as if it is not worth it ?

[gvanrossum]

We can just choose to live with the status quo, can't we?

[kumaraditya303]

We can just choose to live with the status quo, can't we?

That's what I asked, this has proven to be more controversial than I had hoped, the SC advised to deprecate this first hence I created this issue, I'll just close it now as it seems there isn't enough support for this now :(