Fix the compilation failure on DecisionService–Decision output type mismatch

[AthiraHari77]

Currently, compilation fails if the output type of a DecisionService and its contained Decision differ, particularly when the DecisionService is defined as a FunctionItem. This needs to be addressed.

Example:
DecisionService typeRef: dateList
Decision output typeRef: date
Result: Compilation error due to mismatch.
Return type typeRef mismatch while compiling node 'To Singleton List DS'; FunctionItem defines typeRef 'dateList', the defined decision logic defines typeRef 'date'. (DMN id: _BF3F2933-A588-41F1-AC98-492A79088A53, The typeRef does not match

This is not a fundamental type mismatch but a collection difference (single value vs list).
If the DecisionService expects a collection and the Decision provides a single item (or vice versa), coercion should be applied where possible.
The coercion logic should be applied during evaluation to handle such cases consistently.

1157-implicit-conversions.txt