Fix client methods silently swallowing JSON-RPC error responses

[koic]

Motivation and Context

Client methods (tools, resources, resource_templates, prompts, read_resource, get_prompt, call_tool) silently swallowed JSON-RPC error responses by falling back to empty defaults. This did not conform to JSON-RPC 2.0, which clearly distinguishes error responses from success responses. Both the Python SDK (MCPError) and TypeScript SDK (ProtocolError) raise exceptions on error responses. The Ruby SDK was the only one silently discarding them.

Introduces a common request method that handles JSON-RPC request construction and error checking in one place, replacing the duplicated transport.send_request calls across all client methods.

How Has This Been Tested?

Added tests for each affected method verifying that ServerError is raised with the correct code, message, and data attributes.

Breaking Changes

The previous behavior of silently returning empty defaults on server errors did not conform to JSON-RPC 2.0. Error responses should be surfaced to callers, not swallowed. Callers that relied on the silent fallback behavior will need to rescue MCP::Client::ServerError.

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