bugfix: fix crash bug in token cache logic

This change fixes a problem in the token cache logic to avoid panics caused by empty token arrays
by ensuring at least one token remains on full cache hits in the relevant function. The happens
if there is an exact match in the cache on subsequent generations.

x/mlxrunner/cache.go

@@ -78,6 +78,11 @@ func (c *kvCache) findRemaining(tokens []int32) []int32 {
 		prefix++
 	}
 
+	if prefix == len(tokens) && prefix > 0 {
+		// Leave one token to run through the model so we can sample a response.
+		prefix--
+	}
+
 	if prefix < len(c.tokens) {
 		trim := len(c.tokens) - prefix
 		for _, kv := range c.caches {