feat: implement lazy parser

tests/data/bugfix_verify.yml

@@ -0,0 +1,13 @@
+- config:
+    name: basic test with httpbin
+    base_url: https://httpbin.org/
+    verify: False
+
+- test:
+    name: headers
+    request:
+        url: /headers
+        method: GET
+    validate:
+        - eq: ["status_code", 200]
+        - eq: [content.headers.Host, "httpbin.org"]

tests/data/demo_testcase.yml

@@ -1,8 +1,9 @@
 - config:
-    name: "123$var_a"
+    name: "123t$var_a"
     variables:
-        var_a: 0
-        var_c: "${sum_two(1, 2)}"
+        var_a: 1
+        var_b: 2
+        var_c: "${sum_two($var_a, $var_b)}"
         var_d: "${gen_random_string(5)}"
         var_e: $var_d
         PROJECT_KEY: ${ENV(PROJECT_KEY)}