Introduction of the variable prodlnox for EMAC

[FranziskaWinterstein]

The changes introduce the variable prodlnox as the integrated sum of NOxcg and NOxic divided by the timestep length.

Description

The variable is introduced by a fix in emac fixes. It requires NOxcg, NOxic and dt being available in the given channel.

prodlnox will be on dimension [time] only. It is derived as kg s-1 (conversion to the displayed Tg yr-1 per preprocessor possible).

Result looks like this:

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.71%. Comparing base (03b6871) to head (a8af903).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2499 +/- ## ======================================= Coverage 94.70% 94.71% ======================================= Files 249 249 Lines 14114 14123 +9 ======================================= + Hits 13367 13376 +9 Misses 747 747 ```

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