The startup config/manifest reads used PyYAML's pure-Python SafeLoader,
which is ~8x slower than the libyaml-backed CSafeLoader C extension.
config.yaml is parsed several times during launch (cli config, raw
config, early interface/redaction bridge, logging config) and every
plugin manifest is parsed once — all on the slow path.
Add utils.fast_safe_load (CSafeLoader-preferring, pure-Python fallback,
true drop-in for safe_load) and route the hot startup parse sites
through it: hermes_cli/config.py (config + manifest reads),
hermes_cli/plugins.py (manifest parse), env_loader, cli.load_cli_config,
hermes_logging, and the two pre-config early YAML bridges in main.py.
Behavior is identical (same restricted safe tag set); only speed changes.
safe_load calls on the startup path drop from ~79 to ~0, cutting the
YAML parse cost from ~0.9s to ~0.15s under profiling.
Adds tests/test_fast_safe_load.py asserting equivalence with safe_load
across input shapes, empty-doc falsiness, C-loader preference, and that
python/object tags are still rejected (safe, not full loader).
