chore: add gitignore and build configuration

pubspec.yaml

@@ -0,0 +1,15 @@
+name: cellar
+description: A spreadsheet engine with a formula language, dependency graph and CSV IO in pure Dart.
+version: 0.1.0
+publish_to: none
+
+environment:
+  sdk: ^3.13.2
+
+# Add regular dependencies here.
+dependencies:
+  # path: ^1.9.0
+
+dev_dependencies:
+  lints: ^6.0.0
+  test: ^1.31.2