[requests] Type module constants and Response.links

[ekanshul]

REDIRECT_STATI, DEFAULT_REDIRECT_LIMIT, CONTENT_CHUNK_SIZE, ITER_CHUNK_SIZE, utils.DEFAULT_CA_BUNDLE_PATH, hooks.HOOKS, the Response.links property and the return types of hooks.default_hooks() and utils.get_environ_proxies() were Incomplete/Any although their runtime types are fixed: the constants are a tuple of status codes, plain ints, the certs.where() path string and the list of hook names; links maps each parsed Link header's rel (or URL) to the dict[str, str] returned by parse_header_links(); default_hooks() returns a dict of empty lists per hook name; and get_environ_proxies() returns urllib.request.getproxies() or an empty dict.

Agent used: Claude Code

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉