MCP Tool Prefactoring

[jordanstephens]

Description

While working on introducing a CLI agent in #1531, that PR has grown too large. So I'm opening this one to get small refactorings in early:

• factoring out a timeutils package to that we can parse time strings in the cli and in the logs tool handler
• make the tool handlers public—we are about to share them between packages.
• creating a new agent package.
  • moving mcp tools into the agent package. These tool handlers will get refactored for genkit in CLI Agent #1531 and then wrapped to be compatible with mcp-go tool handlers, but moving the files first will make it easier to track changes in CLI Agent #1531.
  • move the mcp "common" code into the agent package.

Linked Issues

Checklist

• I have performed a self-review of my code
• I have added appropriate tests
• I have updated the Defang CLI docs and/or README to reflect my changes, if necessary