Add support for memcached_gat

[thatsafunnyname]

Written by Claude "sonnet" model from Anthropic using these 3 prompts:

• Analyze the source code and the project build files in this directory and all the directories below.
• Add support for the GAT (Get and Touch) commands to both the text and binary protocols, be sure to add test coverage and documentation.
• In the test "gat extends expiration binary=", is a sleep for 2 seconds needed?