feat: add a Close method to transport

[MattDevy]

Adds a Close method to the transport which cleans up resources.

• Closes the client gracefully
  • Cancels running and scheduled background DiscoverNodes calls
  • Cancels scheduled connection resurrections
• Forcefully stops the client on context timeout
• Sets a timeout for DiscoverNodesContext calls from within scheduleDiscoverNodes loop to be equal to the DiscoverNodesInterval. DiscoverNodeTimeout is still respected

[prodsecmachine]

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