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/export_native.py

@@ -9,7 +9,7 @@ from pathlib import Path
 sys.path.insert(0, str(Path(__file__).resolve().parent))
 
 import yaml
-from common import list_registered_platforms, load_platform_config
+from common import list_registered_platforms, load_platform_config, yaml_load
 from exporter import discover_exporters
 
 OUTPUT_FILENAMES: dict[str, str] = {
@@ -60,7 +60,7 @@ def run(
             continue
 
         with open(truth_file) as f:
-            truth_data = yaml.safe_load(f) or {}
+            truth_data = yaml_load(f) or {}
 
         scraped: dict | None = None
         try: