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/base_scraper.py

@@ -9,6 +9,7 @@ import urllib.request
 from abc import ABC, abstractmethod
 from dataclasses import dataclass, field
 from pathlib import Path
+from common import yaml_load
 
 
 @dataclass
@@ -277,7 +278,7 @@ def scraper_cli(
         output_path = Path(args.output)
         if output_path.exists():
             with open(output_path) as f:
-                existing = yaml.safe_load(f) or {}
+                existing = yaml_load(f) or {}
             # Preserve existing keys not generated by the scraper.
             # Only keys present in the NEW config are considered scraper-generated.
             # Everything else in the existing file is preserved.