perf: faster extract_hash_tag (#160)

Author: supercaracal

lib/redis_client/cluster/command.rb

@@ -8,6 +8,8 @@ class RedisClient
   class Cluster
     class Command
       EMPTY_STRING = ''
+      LEFT_BRACKET = '{'
+      RIGHT_BRACKET = '}'
 
       Detail = Struct.new(
         'RedisCommand',
@@ -104,10 +106,11 @@ def determine_optional_key_position(command, option_name) # rubocop:disable Metr
       # @see https://redis.io/topics/cluster-spec#keys-hash-tags Keys hash tags
       def extract_hash_tag(key)
         key = key.to_s
-        s = key.index('{')
-        e = key.index('}', s.to_i + 1)
+        s = key.index(LEFT_BRACKET)
+        return EMPTY_STRING if s.nil?
 
-        return EMPTY_STRING if s.nil? || e.nil?
+        e = key.index(RIGHT_BRACKET, s + 1)
+        return EMPTY_STRING if e.nil?
 
         key[s + 1..e - 1]
       end