Convert tests to @testitem format with TestItemRunner.jl (#25)

Author: Copilot

Project.toml

@@ -21,6 +21,7 @@ julia = "1.10"
 [extras]
 DataFrames = "a93c6f00-e57d-5684-b7b6-d8193f3e46c0"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+TestItemRunner = "f8b46487-2199-4994-9208-9a1283c18c0a"
 
 [targets]
-test = ["DataFrames", "Test"]
+test = ["DataFrames", "Test", "TestItemRunner"]