feat: add insta as dependency

We are going to start to add "golden"/snapshot tests, so we are using
[insta](https://insta.rs) to do so.

crates/aiken-lang/Cargo.toml

@@ -34,4 +34,11 @@ chumsky = { version = "0.9.2", features = ["ahash", "std"], default-features = f
 
 [dev-dependencies]
 indoc = "2.0.1"
+insta = { version = "1.30.0", features = ["yaml"] }
 pretty_assertions = "1.3.0"
+
+[profile.dev.package.insta]
+opt-level = 3
+
+[profile.dev.package.similar]
+opt-level = 3