Get dataclass declaration scope locals with inspect.currentframe()

[noirbee]

inspect.stack() can be very costly, especially when called with
context=1: it has to get information about source files / lines
etc. This gets very slow when using dozens of dataclasses in some
large-ish codebases (where stacks can be relatively deep).

Also add the frame when class_schema() is called directly.

[lovasoa]

Thanks for the pr

[luk2302]

@noirbee @lovasoa This causes quite a significant memory leak due to _internal_class_schema being lru_cache-d and the stack frame therefore being cached and kept alive for a very long time. Especially if there are big locals around when calling class_schema, even only in the calling code way higher up in the stack frame since the f_back properties of the class_frame bubble up and contain the entire stack and all the local variables. If we manually call _internal_class_schema.cache_clear() the memory is freed. You must not insert the clazz_frame into any cache.