perf: read yaml through the c loader

Loading the emulator profiles is the most expensive step of every
command here, and all forty call sites used the pure-Python scanner
while libyaml sat unused in the same wheel. One shared yaml_load picks
the C loader when pyyaml ships it: the 375 profiles parse in 0.18s
instead of 1.39s, and verify --platform retroarch drops from 2.17s to
0.73s. The loader class is the same restricted one safe_load uses.

es_bios.xml was parsed straight from the network while install.py
already refused a document declaring entities; both now share one
guard. Scrapers reach it through a single path bootstrap in the
package rather than two ad-hoc ones.

scripts/scraper/__init__.py

@@ -10,9 +10,18 @@ from __future__ import annotations
 
 import importlib
 import pkgutil
+import sys
 from pathlib import Path
 
-from .base_scraper import BaseScraper
+# Scrapers run both as `python -m scripts.scraper.x` and as plain scripts, and
+# they share helpers with the rest of scripts/. Putting that directory on the
+# path once here is what lets every submodule say `from common import ...`
+# instead of carrying its own bootstrap.
+_SCRIPTS_DIR = str(Path(__file__).resolve().parent.parent)
+if _SCRIPTS_DIR not in sys.path:
+    sys.path.insert(0, _SCRIPTS_DIR)
+
+from .base_scraper import BaseScraper  # noqa: E402
 
 _scrapers: dict[str, type] = {}