Add Excel processing functionality with merge pattern application

- Introduced `index.ts` to read an Excel file and apply merge patterns to specified ranges.
- Created `lib.ts` with utility functions for column number conversion and merge pattern application.
- Updated execution counts in `carbone.ipynb` to reflect the new code structure.

notebooks/excel/lib.ts

@@ -0,0 +1,57 @@
+import { type Worksheet } from "exceljs";
+
+
+/**
+ * Converts an Excel column label to a 1-based number.
+ * Example: A -> 1, Z -> 26, AA -> 27
+ */
+function columnToNumber(label: string): number {
+  let n = 0;
+
+  for (let i = 0; i < label.length; i++) {
+    n = n * 26 + label.charCodeAt(i) - 64;
+  }
+
+  return n;
+}
+
+/**
+ * Generates merge ranges like:
+ * C8:G10, I8:M10, ...
+ * then C14:G16, I14:M16, ...
+ */
+type MergeRangePattern = {
+  startColumns: readonly string[];
+  firstStartRow: number;
+  mergeWidthInColumns: number;
+  mergeHeightInRows: number;
+  mergeBlockCount: number;
+  rowStepBetweenBlocks: number;
+};
+
+export function applyMergePattern(sheet: Worksheet, config: MergeRangePattern) {
+
+  const {
+    startColumns,
+    firstStartRow,
+    mergeWidthInColumns,
+    mergeHeightInRows,
+    mergeBlockCount,
+    rowStepBetweenBlocks
+  } = config;
+
+  for (let block = 0; block < mergeBlockCount; block++) {
+
+    const rowStart = firstStartRow + block * rowStepBetweenBlocks;
+    const rowEnd = rowStart + mergeHeightInRows - 1;
+
+    for (const column of startColumns) {
+
+      const colStart = columnToNumber(column);
+      const colEnd = colStart + mergeWidthInColumns - 1;
+
+      sheet.mergeCells(rowStart, colStart, rowEnd, colEnd);
+
+    }
+  }
+}