test: Enhanced test coverage for McpClientAutoConfigurationRuntimeHintsTests

[alxkm]

Enhanced test coverage for McpClientAutoConfigurationRuntimeHintsTests

Added comprehensive test cases to improve coverage of the McpClientAutoConfigurationRuntimeHints class:

• Test infrastructure: Added @BeforeEach setup and extracted constants for better maintainability
• Idempotency testing: Verifies multiple registration calls don't create duplicates for both reflection and resource hints
• Member category validation: Ensures all MemberCategory values are registered for MCP client types
• Resource pattern verification: Tests for JSON resource pattern registration and persistence
• Nested class validation: Specific tests for McpStdioClientProperties.Parameters registration
• ClassLoader scenarios: Tests with null ClassLoader for typical Spring Boot usage

These additions ensure robust AOT hint registration behavior for MCP client auto-configuration, particularly focusing on JSON resource access and reflection hints required for native compilation.

[sobychacko]

Merged via 0ba1546.