Improve efficiency with manual YAML operations

tests/ef_tests/src/yaml_decode/utils.rs

@@ -22,3 +22,14 @@ pub fn yaml_to_string(yaml: &Yaml) -> String {
 
     out_str
 }
+
+pub fn yaml_split_header_and_cases(mut yaml: String) -> (String, String) {
+    let test_cases_start = yaml.find("\ntest_cases:\n").unwrap();
+    // + 1 to skip the \n we used for matching.
+    let mut test_cases = yaml.split_off(test_cases_start + 1);
+
+    let end_of_first_line = test_cases.find("\n").unwrap();
+    let test_cases = test_cases.split_off(end_of_first_line + 1);
+
+    (yaml, test_cases)
+}