feat(rust,python): add "sql_expr" function

[universalmind303]

closes #8839

[ritchie46]

Nice! Can you also add a docs entry in the python docs?

[universalmind303]

Nice! Can you also add a docs entry in the python docs?

@ritchie46, I havent worked with sphinx before, is it just a matter of updating py-polars/docs/source/reference/expressions/functions.rst to include sql_expr?

[ritchie46]

@ritchie46, I havent worked with sphinx before, is it just a matter of updating py-polars/docs/source/reference/expressions/functions.rst to include sql_ex?

That's it.

[universalmind303]

Should be good to go now.