Add a test to ensure tool list in README is up to date

[kenzieschmoll]

This test should parse the content of the dart_mcp_server package README file and verify that the list of supported tools documented in the README contains all tools provided by the Dart MCP Server. This test should run on presubmits and will prevent the readme from becoming stale.

Another option would be to generate the README based on the list of provided tools and their descriptions, but this may be more work to implement.