[red-knot] Diagnostic for conflicting declared attribute types

[sharkdp]

We should emit a diagnostic when we see conflicting declared types of attributes, either between the declaration in the class body and declarations in a method, or between annotated assignments in different methods. We have existing tests for this scenario (see TODO comments):

ruff/crates/red_knot_python_semantic/resources/mdtest/attributes.md

Lines 212 to 226 in eb08345

	class C:
	z: int
	def __init__(self) -> None:
	self.x = get_int()
	self.y: int = 1
	def other_method(self):
	self.x = get_str()
	# TODO: this redeclaration should be an error
	self.y: str = "a"
	# TODO: this redeclaration should be an error
	self.z: str = "a"

part of: #14164