feat: add SheetStats with GetSheetStats and CalculateSheetStats (E1)

[AdamDrewsTR]

Summary

Add SheetStats struct and methods to compute and cache worksheet data extent statistics.

SheetStats Struct

type SheetStats struct {
    Rows    int    // Total number of rows with data
    Cols    int    // Maximum column index used
    Cells   int64  // Total number of non-empty cells
    MaxCell string // Cell reference of the bottom-right used cell (e.g., "Z100")
}

Methods

• CalculateSheetStats(sheet string) (*SheetStats, error) — Iterates all rows/columns using the Rows iterator, computes statistics, and caches the result. Subsequent calls return the cached value.
• GetSheetStats(sheet string) *SheetStats — Returns previously cached stats without recalculating, or nil if not yet computed.

Usage

f, err := excelize.OpenFile("Book1.xlsx")
if err != nil {
    return err
}
defer f.Close()

stats, err := f.CalculateSheetStats("Sheet1")
if err != nil {
    return err
}
fmt.Printf("Rows: %d, Cols: %d, Cells: %d, MaxCell: %s\n",
    stats.Rows, stats.Cols, stats.Cells, stats.MaxCell)

// Later retrieval without recalculation:
cached := f.GetSheetStats("Sheet1")

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.60%. Comparing base (4bebb61) to head (115c266).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2327   +/-   ##
=======================================
  Coverage   99.60%   99.60%           
=======================================
  Files          32       32           
  Lines       26791    26824   +33     
=======================================
+ Hits        26685    26718   +33     
  Misses         55       55           
  Partials       51       51           

Flag	Coverage Δ
unittests	99.60% <100.00%> (+<0.01%)	⬆️

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