Reduce dimensionality of working arrays in ZDF

Context

• Reference configuration/test case (to add, chosen or used as template)
• Modifications of versioned files: ZDF, TRA/trazdf.F90
• Additional dependencies
• New datasets
• Any other relevant information

Proposal

The aim is to reduce working array dimensions in the ZDF modules.

This refactoring is a form of loop fusion and results in code being moved into fewer, larger loops. Performance can deteriorate if this is done too aggressively, as the loop can contain more branching conditionals (i.e. IF statements). Array dimensionality will be reduced as much as possible without causing this.

Continuation of the work done in #80 (closed).