v0.2.1 of tablex

A production-grade Flutter data grid with zero dependency on any third-party grid engine. Changelog excerpt: ### Bug fixes - WASM compatibility— file import (FilePicker.pickFiles) is now behind a conditional export so dart:iois never imported on web or WASM. dart.library.js_interoproutes to an HTML ``+ FileReaderimplementation instead. - Formatting— all library files now pass dart format. - Dependency lower-bound fix— tightened excelconstraint to ^4.0.6(the version that introduced TextCellValue.valueas TextSpan); the previous ^4.0.0caused a type error[...]