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/bizhawk_scraper.py

@@ -54,8 +54,6 @@ STATUS_RANK = {
     "Ideal": 4,
 }
 
-GAME_DATA_SYSTEMS = {"BSX", "Doom"}
-GAME_DATA_FILES = {"VEC_Minestorm.vec"}
 
 SYSTEM_ID_MAP: dict[str, str] = {
     "32X": "sega-32x",