mv-python

I have an idea. Can we create internals documentation and add it there? Cython codebase is pretty complex so adding details about cython internals to documentation could be useful and...

I did quick look. Section `Auto encoding and decoding` is not migrated to pure python mode. Is it intentional? Also other section in the end are not migrated.

> Yes, see [#4389 (comment)](https://github.com/cython/cython/pull/4389#issuecomment-1883086984) Ah OK. I will have a look on this PR (can take some time). Small changes I will commit directly to this PR and if...

I have fixed the comments by the @scoder. Since, he expressed green light merging this after CI green I will accept the PR. The reset can be done in separate...

> To me `__PYX_ERR` looks fairly simple - it's difficult to see how it could be shrunk (or factored out into a function call) but it may well be worth...

> > But what I did is to do following (stupid and broken) refactor of __PYX_MARK_ERR_POS: > > Doesn't quite work: `__pyx_filename`, `__pyx_lineno`, and `__pyx_clineno` are local variables in most...

> Is it possible to refactor `__PYX_ERR` to function call if it contains goto? But what I did is to do following (stupid and broken) refactor of `__PYX_MARK_ERR_POS`: > >...

> This isn't quite right I think Yes it is possible. Feel free to correct me. I am not 100% sure if I understand correctly everything. My understanding is following:...

> For some reason there's a weird bimodal thing going on here: for 5 extensions the difference is 0.1%-0.2%, and for 3 other ones it's way larger, 5%-8%. I suppose...

> I propose to deprecate all command line options for this and let users control the feature entirely with the C macro. Updated description to reflect it