[ie/youtube] Implement external n/sig solver (#14157)

Closes #14404, Closes #14431, Closes #14680, Closes #14707

Authored by: bashonly, coletdjnz, seproDev, Grub4K

Co-authored-by: coletdjnz <coletdjnz@protonmail.com>
Co-authored-by: bashonly <bashonly@protonmail.com>
Co-authored-by: sepro <sepro@sepr0.com>

yt_dlp/extractor/youtube/jsc/_builtin/quickjs.py

@@ -0,0 +1,59 @@
+from __future__ import annotations
+
+import pathlib
+import shlex
+import subprocess
+import tempfile
+
+from yt_dlp.extractor.youtube.jsc._builtin.ejs import EJSBaseJCP
+from yt_dlp.extractor.youtube.jsc.provider import (
+    JsChallengeProvider,
+    JsChallengeProviderError,
+    JsChallengeRequest,
+    register_preference,
+    register_provider,
+)
+from yt_dlp.extractor.youtube.pot._provider import BuiltinIEContentProvider
+from yt_dlp.utils import Popen
+
+
+@register_provider
+class QuickJSJCP(EJSBaseJCP, BuiltinIEContentProvider):
+    PROVIDER_NAME = 'quickjs'
+    JS_RUNTIME_NAME = 'quickjs'
+
+    def _run_js_runtime(self, stdin: str, /) -> str:
+        if self.runtime_info.name == 'quickjs-ng':
+            self.logger.warning('QuickJS-NG is missing some optimizations making this very slow. Consider using upstream QuickJS instead.')
+        elif self.runtime_info.version_tuple < (2025, 4, 26):
+            self.logger.warning('Older QuickJS versions are missing optimizations making this very slow. Consider upgrading.')
+
+        # QuickJS does not support reading from stdin, so we have to use a temp file
+        temp_file = tempfile.NamedTemporaryFile(mode='w', suffix='.js', delete=False, encoding='utf-8')
+        try:
+            temp_file.write(stdin)
+            temp_file.close()
+            cmd = [self.runtime_info.path, '--script', temp_file.name]
+            self.logger.debug(f'Running QuickJS: {shlex.join(cmd)}')
+            with Popen(
+                cmd,
+                text=True,
+                stdin=subprocess.PIPE,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE,
+            ) as proc:
+                stdout, stderr = proc.communicate_or_kill()
+                if proc.returncode or stderr:
+                    msg = f'Error running QuickJS process (returncode: {proc.returncode})'
+                    if stderr:
+                        msg = f'{msg}: {stderr.strip()}'
+                    raise JsChallengeProviderError(msg)
+        finally:
+            pathlib.Path(temp_file.name).unlink(missing_ok=True)
+
+        return stdout
+
+
+@register_preference(QuickJSJCP)
+def preference(provider: JsChallengeProvider, requests: list[JsChallengeRequest]) -> int:
+    return 850