Add range specifications inside the sheet itself

At present we can import ranges from the spreadsheet.

It ought to be possible to specify the ranges to be imported in the spreadsheet itself.
This would involve defining and documenting the format and building a parser for it.

Start by inspecting the existing spreadsheet range-import path and how imported ranges are represented. Define and document the in-sheet range format, then build a parser that supports it and verify that imports use the specified ranges.

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