Fix worksheet dimensions when XML metadata is incomplete

[lite-tx]

Summary

• update the current row and column when an explicit cell reference is read
• expand the worksheet dimension from every valid loaded cell
• preserve any larger dimension already declared by the worksheet XML

The <dimension> element can be missing or incomplete. Previously, explicit cell references did not update col_num, and a syntactically valid but incomplete dimension prevented the later fallback from recalculating the range. This made cells readable while Worksheet::dimension() still reported an incorrect last column. Tracking explicit references also ensures a following cell without an r attribute is placed in the next column.

Verification

• reproduced incorrect ranges for missing, narrow, and shifted <dimension> elements on current master
• reproduced misplaced cells when explicit and implicit cell references are mixed
• verified the fix with a normal workbook plus five valid ZIP fixtures:
  • missing dimension
  • narrow dimension
  • shifted starting cell
  • mixed explicit/implicit cell and row references
  • an oversized dimension that must not be shrunk
• verified all expected cell values and final dimensions after loading
• built and ran the regression with Qt 5.15.2/MSVC in Debug, Release static, and Release shared configurations
• built and ran the regression with Qt 6.6.0/MSVC in Release static configuration
• built and ran TestExcel through qmake/nmake

Fixes #440

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud