[PR] fix(sheet): keep worksheet substreams paired with their sheets [fesod]

["Sean-Walker0 (via GitHub)" <gi...@apache.org>]

Sean-Walker0 opened a new pull request, #1210:
URL: https://github.com/apache/fesod/pull/1210

   ## Purpose of the pull request
   
   An `.xls` whose workbook-global substream order puts a chart sheet, Excel 4 macro sheet or VB module **before** a worksheet is misread: the worksheet's rows are attributed to the skipped sheet's name/number, later sheets are silently dropped, and when the skipped substream comes first the whole read fails with a `NullPointerException` from the cell handlers (`readSheetHolder()` is null).
   
   No issue exists for this yet; found by code audit of the BIFF substream state machine.
   
   ## What's changed?
   
   Every substream that carries a `BOUNDSHEET` entry occupies a slot in the ordered sheet list — worksheets, charts, macro sheets and VB modules alike (`BoundSheetRecord.orderByBofPosition` orders all of them, and `initReadSheetDataList` builds one `ReadSheet` per entry). `BofRecordHandler` consumed a `readSheetIndex` slot only for `TYPE_WORKSHEET` BOFs and returned early for every other type, so any non-worksheet substream shifted the slot pairing for everything after it, and its own cell records were never marked ignored.
   
   For `TYPE_CHART`, `TYPE_EXCEL_4_MACRO` and `TYPE_VB_MODULE` BOFs the handler now consumes the sheet-list slot and sets `ignoreRecord` — the same treatment the unmatched-worksheet path already applies — so the following worksheets pair with their own `ReadSheet` and the skipped substream's records are filtered by the existing ignorable-handler gate.
   
   ## Checklist
   
   - [x] I have read the [Contributor Guide](https://fesod.apache.org/community/contribution/).
   - [x] I have written the necessary doc or comment.
   - [x] I have added the necessary unit tests and all cases have passed.
   
   ## Verifying this change
   
   `XlsNonWorksheetSubstreamTest` builds a real two-sheet workbook with POI and rewrites the `Workbook` stream so the first sheet substream declares itself as a chart (BOF type `0x0020`) while keeping its cell records — the layout Excel writes when a chart sheet precedes a worksheet:
   
   - `readWorksheetFollowingAChartSubstream` — red before (NPE: `readSheetHolder()` is null in `determineTargetColumnIndex`), green after: `sheet(1)` returns its own data;
   - `readAllSkipsTheChartSubstreamAndKeepsSheetPairing` — red before (same NPE), green after: the worksheet's data lands under `sheet1`, the chart substream contributes nothing;
   - `readUnmodifiedWorkbookWorksAsBefore` — pins ordinary two-sheet reads, green before and after.
   
   - `./mvnw clean package -B -Dmaven.test.skip=false -pl fesod-common,fesod-shaded,fesod-sheet`: 961 tests, 0 failures, 0 errors.
   - `./mvnw -pl fesod-sheet spotless:check`: clean.
   
   ## Notes
   
   - Behavior notes: non-worksheet substreams no longer deliver stray rows into the previously-matched sheet, and a chart/macro/VB sheet now simply reads as empty instead of leaking another sheet's data or crashing. `TYPE_WORKSPACE_FILE` and unknown BOF types keep the old no-op behavior (they carry no `BOUNDSHEET` entry).
   - Orthogonal to open PRs: no open PR touches `BofRecordHandler` or the v03 substream state machine. Related-but-separate: #1201 (this author) guards the trailing `endSheet` for unmatched sheets — on unpatched main, reading only the chart-shifted sheet without a worksheet match would surface that NPE instead; the two fixes are independent and compose.
   - Incidental observation (not touched here): line 65 of `BofRecordHandler` uses `assert` for the sheet lookup, which is a no-op in production; with the slot accounting fixed the index can no longer run past the list, so the assert stays as documentation only.


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