refactor: merge cached_schema_for_type into schema_for_type

[DaleSeo]

Motivation and Context

Following @alexhancock's suggestion in #566 (comment) to consolidate caching logic into the primary public method, this PR applies the same refactoring pattern to schema_for_type and cached_schema_for_type.

Previously, we had two public functions serving the same purpose:

• schema_for_type<T>() -> JsonObject - no caching
• cached_schema_for_type<T>() -> Arc<JsonObject> - with caching

This duplication can create confusion about which to use and led to inefficient Arc-to-JsonObject-to-Arc conversions. Following the pattern established in #566, caching is now an internal optimization detail, not part of the public API.

How Has This Been Tested?

Added a few new unit tests

Breaking Changes

Functionality remains the same with improved performance.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[alexhancock]

Yes, this is the way!