fix: Issue/662

[karel-rehor]

Closes #662

Proposed Changes

Adds to fluxDSL:

• ElapsedFlux.java - function type, to serialize flux method |> elapsed(unit)
• In Flux.java - four ways of using this type
  • elapsed() - with a default ChronUnit.Millis
  • elapsed(ChronoUnit) - to measure the elapsed time in the passed ChronoUnit
  • elapsed(units, ChronoUnit) - to measure the elapsed time in the passed unit count of the passed ChronoUnit
  • elapsed(TimeInterval) - to measure the elapsed time based on the units of the passed TimeInterval
• Tests for these

Checklist

• [x] CHANGELOG.md updated
• [x] Rebased/mergeable
• [x] A test has been added if appropriate
• [x] mvn test completes successfully
• [x] Commit messages are conventional
• [x] Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

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

Project coverage is 88.34%. Comparing base (caaa861) to head (ff71ced).

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #705 +/- ## ============================================ + Coverage 88.33% 88.34% +0.01% - Complexity 779 784 +5 ============================================ Files 173 174 +1 Lines 7078 7088 +10 Branches 389 389 ============================================ + Hits 6252 6262 +10 Misses 699 699 Partials 127 127 ```

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