Provide Access to Source Statistics When Using Subfinder as a library

[meme-lord]

Please describe your feature request:

I would like to be able to access the statistics of sources from the passive agent GetStatistics function. The passive agent isnt accessible from the runner because the name in the struct starts with a lowercase letter which makes it only accessible within the package.

I can think of three possible solutions:

1. Make the passiveAgent accessible by changing the struct.
2. Making a new function in the runner that returns the source statistics from the agent
3. I have to implement my own runner. I don't think this requires any changes to the repo but it does feel like I will be reinventing the wheel a bit here

Describe the use case of this feature:

To be able to monitor errors from sources and raise a log message from my automation as well as disabling sources that have errored out, ran out of credits or blocked me.