yt-dlp: incorrect visibility on parameters

_Params should be public. Submitting a normal dict as a file will mismatch with the TypedDict because the type-checker will infer dict[str,bool] instead of _Params. See the example snippet:

def fetch_channel_info(channel: str) -> tuple[str, str, list[str]]:
    """Return (channel_id, channel_handle, video_ids)."""
    opts = {"quiet": True, "extract_flat": True}

    with yt_dlp.YoutubeDL(opts) as ydl:
        info = ydl.extract_info(channel, download=False)

which results in

     ├╴E Argument of type "dict[str, bool]" cannot be assigned to parameter "params" of type "_Params | None" in function "__init__"
     │     Type "dict[str, bool]" is not assignable to type "_Params | None"
     │       "dict[str, bool]" is not assignable to "_Params"
     │       "dict[str, bool]" is not assignable to "None" basedpyright (reportArgumentType) [48, 27]

Start at the yt-dlp stub for the YoutubeDL entry point, especially its init parameter annotation and the _Params definition. Check how the parameter type is exposed and how a normal dict is inferred by a type checker. Done means the example options dictionary is accepted without the reported argument-type error.