I'm keen to "run onto the spike" and find any big potential performance improvements in pydantic-core while the API can be changed easily.

I'd therefore love anyone with experience of rust and/or pyo3 to have a look through the code and see if I'm doing anything dumb.

Particular concerns:

• The "cast_as vs. extract" issues described in Add performance suggestions to docs PyO3/pyo3#2278 was a bit scary as I only found the solution by chance, are there any other similar issues with pyo3?
• generally copying and cloning values - am I copying stuff where I don't have to? In particular, is input or parts of input (in the case of a dict/list/tuple/set etc.) copied when it doesn't need to be?
• Similarly, could we use a PyObject instead of PyAny or visa-versa and improve performance?
• here and in a number of other implementations of ListInput and DictInput we do a totally unnecessary map, is this avoidable? Is this having a performance impact? Is there another way to give a general interface to the underlying datatypes that's more performance
• The code for generating models here seems to be pretty slow compared to other validators, can anything be done?
• Recursive models are slowing than I had expected, I thought it might be the use of RwLock that was causing the performance problems, but I managed to remove that (albeit in a slightly unsafe way) in simplifying recursive references #32 and it didn't make a difference. Is something else the problem? Could we remove Arc completely?
• lifetimes get pretty complicated, I haven't even checked if get a memory leak from running repeat validation, should we/can we change any lifetimes?

I'll add to this list if anything else comes to me.

More generally I wonder if there are performance improvements that I'm not even aware of? "What you don't know, you can't optimise"

@pauleveritt @robcxyz