Remove an uncommitted worksheet from the streaming writer

Cluster: streaming

Reported as "Delete sheet before streaming write".

Desired behavior

The streaming, incremental xlsx writer should expose a supported way to remove a worksheet that has been added to the workbook but has not yet been committed to the output stream.

• If a worksheet has never had any content committed, removing it should leave the finalized workbook as if that sheet was never added: no sheet entry, no orphaned relationship, no gap in sheet ordering, and correct sheetId and index bookkeeping for the remaining sheets.
• Attempting to remove a worksheet that has already been committed must fail loudly, because streaming output is append-only and you cannot un-write bytes already flushed. The error should clearly state that the sheet was already committed.
• Removal should be addressable the same way sheets are otherwise referenced, by worksheet handle, name or id, not by manipulating a private array.

Prior art / why it's not trivial

The streaming writer commits worksheet XML incrementally to keep memory flat, which is why the classic in-memory "remove sheet" operation isn't directly available. The historically-suggested workaround was to splice the entry out of the writer's private internal worksheets collection, which bypasses relationship, content-type and ordering bookkeeping and is unsupported and brittle.

Open questions

• Should removal be an explicit removeWorksheet(...) on the streaming writer, or expressed as the worksheet never being committed, a discard-on-empty?
• Should the writer optionally auto-drop worksheets that were added but never received any committed rows at finalize time, or only remove on explicit request?
• Interaction with defined names, shared formulas, or cross-sheet references that pointed at the removed sheet: reject the removal, or leave dangling refs to the caller?