Add basic test entry point for Gleeunit

Introduces THE ENTRY POINT test file 'sparkling_test.gleam' with a main function that runs Gleeunit tests. This sets up the project for running automated tests.

Author: lupodevelop

test/sparkling_test.gleam

@@ -0,0 +1,5 @@
+import gleeunit
+
+pub fn main() {
+  gleeunit.main()
+}