`NodeCountMapper` doesn't count nodes inside functions

[majosm]

Comparing my concatenation changes with main reminded me that NodeCountMapper doesn't currently accumulate node counts from functions into the overall count. It should be given a map_function_definition method that does something similar to CallSiteCountMapper:

pytato/pytato/analysis/__init__.py

Lines 435 to 446 in 78b43c1

	@memoize_method
	def map_function_definition(self, /, expr: FunctionDefinition,
	*args: Any, **kwargs: Any) -> None:
	if not self.visit(expr):
	return
	new_mapper = self.clone_for_callee(expr)
	for subexpr in expr.returns.values():
	new_mapper(subexpr, *args, **kwargs)
	self.count += new_mapper.count
	self.post_visit(expr, *args, **kwargs)

I wonder if the default map_function_definition implementation in CachedWalkMapper should be disabled, to avoid bugs like this? Maybe a default implementation could be provided in a separate method, e.g. _basic_map_function_definition, for convenience in mappers that don't need special behavior.