Respect the cardinality of before_iteration clauses in the interpreter

[zprobst]

In the interpreter component, you can specify two different blocks of interpretations. interpretations and before_iteration. The before_iteration block is applied for a record is broken down into sub-records and applied to the interpretations block.

Users can also specify lists of lists of interpretations in the interpretations block. Because both the interpreations block and before_iteration block are parsed and loaded the same way, its possible to supply a list of lists to the before_iteration block. However that is not respected in anyway. This provides a confusing experience to users that try and use this.

To resolve this, this PR iterates over each sublist in before_iteration If provided, and performs the iteration and interpretation based on the output of each sublist provided. This creates an experience consistent with the use of the interpretation block.

[codecov]

Codecov Report

Merging #73 (9e5e682) into main (0ee9ca8) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #73   +/-   ##
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  Coverage   93.73%   93.73%           
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  Files         121      121           
  Lines        3032     3032           
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  Hits         2842     2842           
  Misses        190      190           

Flag	Coverage Δ
3.10	93.73% <100.00%> (ø)
3.11	93.73% <100.00%> (ø)

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Files Changed	Coverage Δ
nodestream/interpreting/interpreter.py	97.14% <100.00%> (ø)