fix(clippy): box OAuthFlows and use slice::contains

Two clippy errors caught only with `--all-features -- -D warnings`:

- large_enum_variant: SecurityScheme::OAuth2 carried OAuthFlows directly
  (~817 bytes); other variants ~97 bytes. Box it so the enum's variants
  are similarly sized.
- manual_contains: schema_types.iter().any(|t| *t == X) → contains(&X).

Plus drop the only `expect_used` in catalog-gen.rs by replacing the
`get_mut(...).expect(...)` with an `if let Some(...)` guard.

`cargo clippy --all-features -- -D warnings` is now clean.

Refs #14

Author: lightsofapollo

src/bin/catalog-gen.rs

@@ -211,13 +211,11 @@ fn parse(md: &str) -> Catalog {
                 continue;
             }
             if let Some(field) = parse_field_row(line) {
-                let entry = catalog
-                    .objects
-                    .get_mut(object)
-                    .expect("object inserted on heading");
-                match kind {
-                    TableKind::Fixed => entry.fields.push(field),
-                    TableKind::Patterned => entry.patterned_fields.push(field),
+                if let Some(entry) = catalog.objects.get_mut(object) {
+                    match kind {
+                        TableKind::Fixed => entry.fields.push(field),
+                        TableKind::Patterned => entry.patterned_fields.push(field),
+                    }
                 }
             }
         }

src/openapi.rs

@@ -446,7 +446,10 @@ pub enum SecurityScheme {
     },
     #[serde(rename = "oauth2")]
     OAuth2 {
-        flows: OAuthFlows,
+        // Boxed to keep the SecurityScheme enum's variants similarly sized
+        // (the OAuthFlows tree is ~800 bytes; clippy::large_enum_variant
+        // flagged the disparity).
+        flows: Box<OAuthFlows>,
         #[serde(default)]
         description: Option<String>,
         /// 3.2 §"Security Scheme Object" — well-known metadata URL (D4).
@@ -600,7 +603,7 @@ impl Schema {
     pub fn type_array_contains_null(&self) -> bool {
         match self {
             Schema::TypedMulti { schema_types, .. } => {
-                schema_types.iter().any(|t| *t == SchemaType::Null)
+                schema_types.contains(&SchemaType::Null)
             }
             _ => false,
         }