Remove StringBuilder in Logback TimestampConverter

[KarstenSchnitter]

TimestampConverter in cf-java-logging-support-logback contains the following code:

    @Override
    public String convert(ILoggingEvent event) {
        StringBuilder appendTo = new StringBuilder();
        Instant now = Instant.now();
        long timestamp = now.getEpochSecond() * 1_000_000_000L + now.getNano();
        appendTo.append(timestamp);
        return appendTo.toString();
    }

Creating the StringBuilder is a time consuming implementation for creating a string representation of the long timestamp. This should be changed to a more efficient implementation.

[wolches]

Is this issue actual yet?

[KarstenSchnitter]

@wolches Yes, this is a current open issue. I came across it during a small performance analysis of the library. Since the code is executed for every emitted message, improvements have a larger impact.

[KarstenSchnitter]

Resolved by #97