Extended functionality for LazyExpr UDF

Change function signature to pass metadata of input/output (such as shape) to enable more complicated functions. For example, if the UDF knows both shape and offset, can tell when the chunk is at the edge of the array, and adapt the calculation if necessary.

Start at the LazyExpr UDF entry point and inspect its current function signature. Work out how input and output metadata, including shape and offset, should be exposed, and define completion as allowing a UDF to detect edge chunks and adapt its calculation.

Scritto dal modello di indicizzazione a partire dal testo della issue.