`.pyi` from third party stubs packages should take precedence over bundled `.pyi` files

[jorenham]

This docstring suggests that currently bundled .pyi are prioritized over those from third party stubs packages:

type_coverage_py/analyzer/typeshed_checker.py

Lines 30 to 31 in 1fac224

	def merge_files_with_stubs(package_files: list[str], typeshed_stubs: list[str]) -> list[str]:
	"""Merge package files with typeshed stubs, preferring .pyi files from the package itself."""

But this is at odds with the typing spec: https://typing.python.org/en/latest/spec/distributing.html#import-resolution-ordering

This can affect the coverage of e.g. scipy, which bundles a couple of incomplete .pyi that in scipy-stubs are actually complete.

A more extreme example would be numtype, which intends to override all of numpy's bundled stubs with its own numpy-stubs.