fix #2587

• /channels に path パラメーターをつけたときの動作を修正した.
  • チャンネルが存在しないときに 404 NotFound を返すようにした.
  • 返される値の型が, path パラメーターが無いときと同になるようにした.
• /channels?path= のテストを追加した.

Summary by Copilot

This pull request includes several changes to the router/v3/channels.go file to improve the handling of channel paths and error responses, as well as updates to the corresponding tests. The most important changes include adding error handling for invalid channel paths, modifying the response structure, and enhancing the test coverage for these scenarios.

Error Handling Improvements:

• Added error handling for invalid channel paths in GetChannels function, returning a 404 Not Found status when the path is invalid.

Response Structure Modifications:

• Modified the response structure in GetChannels function to properly format channels and include subchannels in the response. [1] [2]

Test Coverage Enhancements:

• Added a new helper function CreateSubchannel in router_test.go to create subchannels for testing purposes.
• Updated the TestHandlers_GetChannels test function to include checks for subchannels and validate the new error handling for invalid paths. [1] [2] [3] [4] [5]

These changes ensure that the channel handling logic is more robust and that the test suite accurately reflects the new behavior.