feat: Add connection-retry logic with exponential backoff

[scarmuega]

Networks errors or node restarts are common scenarios in long-running operations. Under certain circumstances, the Cardano node might take a while before exposing the corresponding sockets for inbound connections. Upon initialization, if Oura isn't able to connect to the specified Cardano node, it will exit immediately with the corresponding error message.

This PR implements a configurable retry logic that will execute several connection attempts to avoid exiting prematurely if the Cardano node is still initializing. There's a delay between each attempt to avoid stressing the network stack. This delay increases exponentially up to a configurable max value.

Example configuration:

[source.retry_policy]
connection_max_retries = 3
connection_max_backoff = 20 # in seconds

closes #201