feat: add XLSM (Excel Macro-Enabled Workbook) parsing support

[longway-code]

Closes 4047

XLSM files have the same structure as XLSX but can contain VBA macros.
This implementation safely extracts only data content, macros are ignored.

• Add FileType.XLSM enum with correct MIME type
• Update ZipFileDetector to distinguish XLSX from XLSM by extension
• Add partition_xlsm() function that wraps partition_xlsx()
• Add test suite with 17 tests
• Create 5 XLSM test files for different scenarios
• Maintain full backward compatibility with XLSX