fix: resolve all cargo clippy warnings

- Fix toml version requirement metadata warning
- Replace clone() with std::slice::from_ref()
- Collapse nested if statements
- Add #[allow(dead_code)] to test utility functions
- Fix unused imports and variables in tests
- Use unwrap_or_else instead of expect with format!

wtismycode-core/Cargo.toml

@@ -6,7 +6,7 @@ edition = "2024"
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
-toml = "0.9.11+spec-1.1.0"
+toml = "0.9.11"
 tracing = "0.1"
 anyhow = "1.0"
 thiserror = "2.0.18"