Add global memo cache and eviction API

[nicholasjng]

As per this TODO:

nnbench/src/nnbench/types/types.py

Lines 104 to 119 in 65fc45b

	class Memo(Generic[T]):
	@functools.cache
	# TODO: Swap this out for a local type-wide memo cache.
	# Could also be a decorator, should look a bit like this:
	# global memo_cache, memo_cache_lock
	# _tid = id(self)
	# val: T
	# with memocache_lock:
	# if _tid in memo_cache:
	# val = memo_cache[_tid]
	# return val
	# val = self.compute()
	# memo_cache[_tid] = val
	# return val
	def __call__(self) -> T:
	raise NotImplementedError

Steps are

1 - bring back the global cache + lock,
2 - insert values based on the id of the inserting memo,
3 - add a clear_memo_cache API, maybe factoring out everything related into a nnbench.types.memo submodule.
4 - (optional) - check if evicting the memoized value in Memo.del() does anything (debug logs!)
5 - drop functools.cache decorators everywhere (examples!)

NB: Check that the Memo.__call__() type annotation is not affected by the solution, since that breaks typechecking in benchmarks. (With a decorator, this should not be a problem.)

What would be super nice: Showcase a parametrized benchmark with a collection of large numpy array memos, checking if evicting an array after the last run of the family and triggering GC (gc.collect()) does anything. memray is (hopefully) your friend: https://bloomberg.github.io/memray/index.html
-> This needs #125.