feat: relax outputSchema to accept non-object JSON Schema types (SEP-2106) (#895)

* fix: address PR review - schema_for_output no longer validates or returns Result

- Add strip_output() that strips title/description without validating type (Dale #1)
- Change schema_for_output to return Arc<JsonObject> instead of Result (Dale #2)
- Cache only Arc<JsonObject> success values, not Result (Dale #3)
- Remove dead unwrap_or_else panic paths in with_output_schema, ToolBase, and macros
- Tighten test assertions from contains to assert_eq on type field (Dale #4)
- Update test_schema_for_output_rejects_primitive to accept_primitive (SEP-2106)

Co-authored-by: Orca <help@stably.ai>

* test(rmcp): add non-object output schema tests for SEP-2106

Add tests verifying schema_for_output accepts non-object types:
- test_tool_builder_methods: primitive (i32), array (Vec<String>), option
- test_structured_output: tool returning Json<Vec<T>> and Json<i32>
- test_json_schema_detection: Json<Vec<T>>, Result<Json<Vec<T>>,E>, Json<String>
- tool_traits: ToolBase::output_schema with Vec<AddOutput> output type

* test(rmcp): add missing edge case tests from code review

Add tests identified during code review:
- description stripping for primitive types
- composition types (Option<String> with anyOf/oneOf/null)
- cache correctness (Arc::ptr_eq for repeated calls)
- schema_for_input rejecting array types (not just primitives)
- schema_for_output accepting unit type ()

* feat!: mark schema_for_output return-type change as breaking

This introduces SEP-2106: schema_for_output no longer validates or
returns Result. The public signature changed, so bump major.

* fix: address Dale's PR review - direct schema.get assertions, remove ArrayTool

- Replace loose schema_str.contains(...) assertions with direct
  schema.get("type") equality checks in test_tool_builder_methods.rs
  and test_structured_output.rs
- Remove redundant ArrayTool fixture and its round-trip
  serde_json::from_str test from tool_traits.rs since schema is
  already Arc<JsonObject>
- Drop dead schema_str variable in test_structured_output.rs

---------

Co-authored-by: Brandon Bennett <brandonbennett@macbookair.myfiosgateway.com>
Co-authored-by: Orca <help@stably.ai>
Co-authored-by: Brandon Bennett <brandonbennett@Pursuits-Air.lan>

crates/rmcp/tests/test_tool_builder_methods.rs

@@ -22,10 +22,8 @@ fn test_with_output_schema() {
 
     assert!(tool.output_schema.is_some());
 
-    // Verify the schema contains expected fields
-    let schema_str = serde_json::to_string(tool.output_schema.as_ref().unwrap()).unwrap();
-    assert!(schema_str.contains("greeting"));
-    assert!(schema_str.contains("is_adult"));
+    let schema = tool.output_schema.as_ref().unwrap();
+    assert_eq!(schema.get("type"), Some(&serde_json::json!("object")));
 }
 
 #[test]
@@ -57,7 +55,51 @@ fn test_chained_builder_methods() {
     assert!(input_schema_str.contains("name"));
     assert!(input_schema_str.contains("age"));
 
-    let output_schema_str = serde_json::to_string(tool.output_schema.as_ref().unwrap()).unwrap();
-    assert!(output_schema_str.contains("greeting"));
-    assert!(output_schema_str.contains("is_adult"));
+    let output_schema = tool.output_schema.as_ref().unwrap();
+    assert_eq!(
+        output_schema.get("type"),
+        Some(&serde_json::json!("object"))
+    );
+}
+
+#[test]
+fn test_with_output_schema_primitive() {
+    let tool = Tool::new("test", "Test tool", JsonObject::new()).with_output_schema::<i32>();
+
+    assert!(tool.output_schema.is_some());
+
+    let schema = tool.output_schema.as_ref().unwrap();
+    assert_eq!(schema.get("type"), Some(&serde_json::json!("integer")));
+    // title should be stripped from output schema
+    assert!(schema.get("title").is_none());
+}
+
+#[test]
+fn test_with_output_schema_array() {
+    let tool =
+        Tool::new("test", "Test tool", JsonObject::new()).with_output_schema::<Vec<String>>();
+
+    assert!(tool.output_schema.is_some());
+
+    let schema_str = serde_json::to_string(tool.output_schema.as_ref().unwrap()).unwrap();
+    assert!(schema_str.contains("\"type\":\"array\""));
+    assert!(schema_str.contains("items"));
+    // title should be stripped from output schema
+    assert!(!schema_str.contains("title"));
+}
+
+#[test]
+fn test_with_output_schema_option() {
+    let tool =
+        Tool::new("test", "Test tool", JsonObject::new()).with_output_schema::<Option<String>>();
+
+    assert!(tool.output_schema.is_some());
+
+    let schema_str = serde_json::to_string(tool.output_schema.as_ref().unwrap()).unwrap();
+    // Option<String> generates a composition schema (anyOf/oneOf/type array with null)
+    assert!(
+        schema_str.contains("anyOf") || schema_str.contains("oneOf") || schema_str.contains("null"),
+        "Expected composition schema for Option<String>, got: {schema_str}"
+    );
+    assert!(!schema_str.contains("title"));
 }