Use macro per-test-file

Signed-off-by: Marcel Müller <neikos@neikos.email>

tests/cases/multiple.1-parsed.snap

@@ -0,0 +1,28 @@
+---
+source: tests/file_tests.rs
+expression: parsed
+info:
+  input: "Hi there! My name is {{= name }} {{= lastname }}"
+  context:
+    name: Hemera
+    lastname: Green
+---
+ParsedTemplate {
+    tokens: [
+        [Content]"Hi there! My name is" (0..20),
+        [Whitespace]" " (20..21),
+        [LeftDelim]"{{" (21..23),
+        [WantsOutput]"=" (23..24),
+        [Whitespace]" " (24..25),
+        [Ident]"name" (25..29),
+        [Whitespace]" " (29..30),
+        [RightDelim]"}}" (30..32),
+        [Whitespace]" " (32..33),
+        [LeftDelim]"{{" (33..35),
+        [WantsOutput]"=" (35..36),
+        [Whitespace]" " (36..37),
+        [Ident]"lastname" (37..45),
+        [Whitespace]" " (45..46),
+        [RightDelim]"}}" (46..48),
+    ],
+}