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/refresh_data_dirs.py

@@ -23,6 +23,7 @@ import urllib.error
 import urllib.request
 import zipfile
 from pathlib import Path
+from common import yaml_load
 
 try:
     import yaml
@@ -45,7 +46,7 @@ def load_registry(registry_path: str = DEFAULT_REGISTRY) -> dict[str, dict]:
     if not path.exists():
         raise FileNotFoundError(f"Registry not found: {registry_path}")
     with open(path) as f:
-        data = yaml.safe_load(f) or {}
+        data = yaml_load(f) or {}
     return data.get("data_directories", {})