Reduce default size of diagnostic buffer for FlightRecorderInputStream from 1MiB to 1KiB

[dwnusbaum]

Refiling jenkinsci/remoting#770 against the duplicated class here.

Testing done

I added a new test to cover the FlightRecorderInputStream diagnostics for the CLI.

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[dwnusbaum]

I originally was going to put this in the CLI module's unit tests, but without LoggerRule I had no way to write any assertions related to the FlightRecorderInputStream diagnostics.

[jglick]

We could probably just get rid of the recorder in the CLI. I doubt it has ever been used. (The protocol is far simpler than that of Remoting anyway.)