Cache for parsed, immutable per-load-balancer options.

Algorithms with configurable options (LeastCpu, WeightedRoundRobin, HashRing) call init/2 once during boot and stash the parsed config here so subsequent choose_from_nodes calls don't re-parse keyword lists on every selection.

Backed by Cache.PersistentTerm because entries are written once at boot and read on every selection — exactly the access pattern :persistent_term is designed for. Mutable runtime state (e.g. the hash ring rebuilt on every node-change event) lives in dedicated ETS-backed caches instead.