v0.12.1

Fixed

• Sheet-qualified ranges are accepted (#30) — reported by @braklo. parse_range_string had no room for a sheet prefix, so Summary.D4:D6 and every variant were rejected outright and no Calc tool could address anything but the active sheet. Cross-sheet work had to route through switch_sheet, a stateful operation that moves the active sheet under the user, and a chart could not be built over data sitting on a data sheet — the ordinary workbook layout. All four syntaxes now resolve: Sheet1.A1:C5, 'Sheet One'.A1, Sheet1!A1, 'Sheet One'!A1. Supported by calc_read_range, calc_write_range, calc_clear_range, calc_comment and calc_chart; a prefix wins over sheet_name, and disagreeing between the two is an error rather than a silent choice
• Sheet names are no longer upper-cased in errors (#30) — the parser upper-cased the whole reference, so a sheet called Summary was reported back as SUMMARY. Only the address part is normalised now, and an unknown sheet lists the ones that exist
• Invalid Calc input no longer logs as an error — an unknown sheet or a malformed address is the caller's mistake, not a fault, and logging it at ERROR buried the real ones