perf(cache): sort-based eviction and consistent non-positive TTL handling

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.

cache/redis/wrapper.go

@@ -16,7 +16,10 @@ type CacheWrapper struct {
 // NewCacheWrapper creates a new cache wrapper
 func NewCacheWrapper(config *RedisConfig, logger *libpack_logger.Logger) *CacheWrapper {
 	if logger == nil {
-		logger = &libpack_logger.Logger{}
+		// Use the proper constructor, not a zero-value &Logger{} -- its
+		// timeFormat field is a nil atomic.Pointer, so a zero-value Logger
+		// panics on the first log call instead of degrading gracefully.
+		logger = libpack_logger.New()
 	}
 	return &CacheWrapper{
 		redis:  config,