gh-125063: Emit slices as constants in the bytecode compiler (#125064)

* Make slices marshallable

* Emit slices as constants

* Update Python/marshal.c

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>

* Refactor codegen_slice into two functions so it
always has the same net effect

* Fix for free-threaded builds

* Simplify marshal loading of slices

* Only return SUCCESS/ERROR from codegen_slice

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Co-authored-by: Mark Shannon <mark@hotpy.org>
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>