fix: exclude read_excel from browser bundle (uses node:zlib)

read_excel.ts uses `node:zlib` which has no browser polyfill. This caused
the `bun build --target browser` step to fail in CI. Removed read_excel
from barrel exports (src/index.ts, src/io/index.ts) — users who need it
in Node/Bun can import directly from "tsb/io/read_excel". Updated
read_excel.test.ts to import from the module file.

Agent-Logs-Url: https://github.com/githubnext/tsessebe/sessions/fa19ae27-a6ef-46a6-a974-a3c323b8b6a2

Co-authored-by: mrjf <180956+mrjf@users.noreply.github.com>

Author: Copilot

src/index.ts

@@ -469,8 +469,7 @@ export type {
 // PR #120 unique modules — re-exported from sub-barrels
 export { astypeSeries, astype, castScalar } from "./core/index.ts";
 export type { AstypeOptions, DataFrameAstypeOptions } from "./core/index.ts";
-export { readExcel, xlsxSheetNames } from "./io/index.ts";
-export type { ReadExcelOptions } from "./io/index.ts";
+// readExcel / xlsxSheetNames use node:zlib — import from "tsb/io/read_excel" directly
 export { clipAdvancedSeries, clipAdvancedDataFrame } from "./stats/index.ts";
 export type {
   SeriesBound,

src/io/index.ts

@@ -10,5 +10,6 @@ export { readJson, toJson } from "./json.ts";
 export type { ReadJsonOptions, ToJsonOptions, JsonOrient } from "./json.ts";
 export { jsonNormalize } from "./json_normalize.ts";
 export type { JsonPath, JsonNormalizeOptions } from "./json_normalize.ts";
-export { readExcel, xlsxSheetNames } from "./read_excel.ts";
-export type { ReadExcelOptions } from "./read_excel.ts";
+// readExcel / xlsxSheetNames use node:zlib and cannot be bundled for the
+// browser.  Import them directly from "tsb/io/read_excel" when running in
+// Node / Bun.

tests/io/read_excel.test.ts

@@ -3,7 +3,8 @@
  */
 import { describe, expect, it } from "bun:test";
 import fc from "fast-check";
-import { DataFrame, readExcel, xlsxSheetNames } from "../../src/index.ts";
+import { DataFrame } from "../../src/index.ts";
+import { readExcel, xlsxSheetNames } from "../../src/io/read_excel.ts";
 
 // ─── minimal XLSX fixture builder ─────────────────────────────────────────────