ENH: implement `FrozenDict` with `frozendict` #31

Job	Run time
lock / Find lock files	5s
lock / Check if PR already exists	0s
lock / pixi.lock	0s
lock / Determine Python versions	0s
lock / Manifest.toml	0s
lock / .pre-commit-config.yaml	1s
lock / uv.lock	1s
lock / pip constraint files	0s
lock / Push changes	3s
lock / Create PR	1s
	11s

Provide feedback