The count-based evictOldest used an O(n squared) selection sort with a
candidate cap over an unordered map range, so it could evict the wrong
entries. It now collects all entries and sorts by expiry, matching the
memory-based evictor.
A non-positive CACHE_TTL behaved differently per backend: the standard
memory cache panicked, Redis stored a permanent key, and the LRU cache
expired entries immediately. Each backend now clamps a non-positive TTL
to a shared default at its Set boundary. The nil-logger fallback in the
Redis wrapper now uses the constructor so it cannot panic.
lukaszraczylo