fix: Add unit test related to sshnpd

[sitaram-kalluri]

- What I did

• Added a unit test to notify an ssh_request to sshnpd and assert the payload in the notification value.

- How I did it

• When invoking the SshnpDartPureImpl.run() method, the method call await callInitialization(); initializes both the sshnpd and sshrvd channels, which leads to the creation a lot of unnecessary mock objects in the test scenario. To address this, the 'notify' call was moved to a separate method, sendSshRequestToSshnpd, to facilitate easier unit testing.
• In the unit test,
  • Invoke sshnp.srvdChannel.initialize() which will fetch the host and ports from srvd.
  • Then, invoke sshnp.sendSshRequestToSshnpd() which will build the notification key - 'ssh_request` and payload as notification value which is sent to sshnpd.
  • Assert the payload in the mockNotificationService callback.

- How to verify it

• All tests should pass.

[gkc]

LGTM thank you @sitaram-kalluri