DPL: use new indices methods to navigate through InputRecord in output-proxy

[ehellbar]

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[ehellbar]

@ktf here I don't know what the intention of the loop and looping direction was in the first place, so I tried to keep it like that using the new methods you implemented when you refactored the InputRecord.

the old loop and methods were simply way to slow after we went away from the MessageSet, it was simply hidden before by the issues and slow-down we had in the QC task in front.

I might also check the code if there are other places (e.g. detector code) which look suspicious.

[ehellbar]

also, if there is a more elegant way to do this that I don't see right now, please let me know :)

[ktf]

This is to solve a performance regression in the proxy, correct? LGTM for now.

[ehellbar]

yes, the regression is in the dpl-output-proxy. Thank you for reviewing it.