[networking] Add response extensions for impersonate info

[bashonly]

this can be useful during extractor error handling, e.g. in the crunchyroll extractor, where we want to expect the 403 error and a offer a cloudflare bypass hint if impersonation was not used, or else raise w/ a bug report message if impersonation was used.

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[pukkandan]

Pls explain motivation for 3b48105. I liked the first impl much better

[bashonly]

@pukkandan

hypothetically, the value of impersonate can be None:

yt-dlp/yt_dlp/networking/impersonate.py

Lines 61 to 80 in 52f5be1

	class ImpersonateRequestHandler(RequestHandler, ABC):
	"""
	Base class for request handlers that support browser impersonation.
	This provides a method for checking the validity of the impersonate extension,
	which can be used in _check_extensions.
	Impersonate targets consist of a client, version, os and os_ver.
	See the ImpersonateTarget class for more details.
	The following may be defined:
	- `_SUPPORTED_IMPERSONATE_TARGET_MAP`: a dict mapping supported targets to custom object.
	Any Request with an impersonate target not in this list will raise an UnsupportedRequest.
	Set to None to disable this check.
	Note: Entries are in order of preference
	Parameters:
	@param impersonate: the default impersonate target to use for requests.
	Set to None to disable impersonation.
	"""

so if a response is an instance of ImpersonateResponse, then that is completely meaningless on its own. In order to determine if impersonation was used for a request, the extractor would also have to do check truthiness of the impersonate attribute, with the code looking like this:

from ..networking.impersonate import ImpersonateResponse

try:
    ...
except ExtractorError as e:
    if isinstance(e.cause, HTTPError) and e.cause.status == 403:
        if isinstance(e.cause.response, ImpersonateResponse) and e.cause.response.impersonate is not None:
            target = str(e.cause.response.impersonate)
            # handling for impersonation
        # handling for no impersonation

vs. with new impl:

try:
    ...
except ExtractorError as e:
    if isinstance(e.cause, HTTPError) and e.cause.status == 403:
        if target := e.cause.response.extras.get('impersonate'):
            # handling for impersonation
        # handling for no impersonation

[pukkandan]

Why not target := getattr(e.cause.response, 'impersonate', None)?

Alternatively, we could put an impersonate = None in normal Response if we wanna be able to check e.cause.response.impersonate safely

[bashonly]

Why not target := getattr(e.cause.response, 'impersonate', None)?

That should suffice, yeah. I've reverted to the orig impl (but kept the corrected type annotations)

Alternatively, we could put an impersonate = None in normal Response if we wanna be able to check e.cause.response.impersonate safely

IMO the base Response shouldn't concern itself with the extensions of its subclasses