Replace yaml.safe_load / yaml.Dumper with the C extension equivalents
(yaml.CSafeLoader, yaml.CDumper) for all YAML parsing and serialisation
in the virtual repo merge path. A module-level try/except falls back to
the pure-Python SafeLoader/Dumper when libyaml is not available.
Measured on 19-member helm-all (real upstream data):
Before (SafeLoader + Dumper): merge=38,877ms
After (CSafeLoader + CDumper): merge=9,625ms (4.0x faster)
Local microbenchmark (500 charts × 10 versions × 19 members):
Before: 40.8s After: 6.1s (6.7x faster)
unkinben
b7488fce10