Summary

This PR fixes issue #2961 where Excel files generated by tools
like DataGrip/IDEA fail to load due to missing r attributes on
<row> and <cell> elements.

Problem: When parsing Excel files without r attributes, the
library throws "Invalid row number in model" error because the
parser expects explicit row and cell references.

Solution:

• Added currentAddress tracking system to RowXform class
• Automatically generate missing r attributes based on
  sequential position
• Reset column counter at the start of each row
• Maintain full backward compatibility with existing files

Changes:

• lib/xlsx/xform/sheet/row-xform.js: Added address tracking
  logic and automatic r attribute generation
• spec/integration/issues/issue-2961-missing-r-attribute.spec.j
  s: Added comprehensive test case
• spec/integration/data/test-issue-2961.xlsx: Added test data
  file from DataGrip

Test plan

Test Results:

# Run specific test for this issue
$ npx mocha --require spec/config/setup
spec/integration/issues/issue-2961-missing-r-attribute.spec.js
  github issues
    ✓ issue 2961 - Invalid row number in model when r attribute
missing

  1 passing (17ms)

# Run all integration tests
$ npm run test:integration
  195 passing (2s)
  1 failing  # Pre-existing issue #1328, unrelated to this change

Backward Compatibility Test:

• All existing integration tests continue to pass (no
  regressions)
• Files with existing r attributes work unchanged
• Files missing r attributes now parse correctly

Manual Testing:

• ✅ DataGrip-generated Excel file now loads successfully
• ✅ Cells are parsed in correct positions (A1, B1, C1, A2, B2,
  C2)
• ✅ Cell values and types are preserved correctly

Related to source code (for typings update)

Core Implementation:

• https://github.com/exceljs/exceljs/blob/master/lib/xlsx/xform/s
  heet/row-xform.js#L86-L100 - Added automatic r attribute
  generation
• https://github.com/exceljs/exceljs/blob/master/lib/xlsx/xform/s
  heet/row-xform.js#L64-L84 - Added address tracking logic

Test Coverage:

• https://github.com/exceljs/exceljs/blob/master/spec/integration
  /issues/issue-2961-missing-r-attribute.spec.js - Verifies fix
  works correctly

Closes #2961,#2075