test: Add comprehensive test coverage for Ollama runtime hints registration

[alxkm]

Adds new test cases to strengthen OllamaRuntimeHintsTests:

• Null ClassLoader handling - Ensures registration works with null ClassLoader (AOT scenario)
• Basic validation - Verifies hints are actually registered
• Idempotent registration - Prevents duplicate hints on multiple calls
• Main API classes validation - Confirms core Ollama classes are registered
• Package validation - Ensures JSON classes found from correct package
• Hint count control - Prevents excessive registrations that impact build time
• Nested class support - Validates Tool and other nested classes are registered

These tests catch potential native compilation failures and ensure proper AOT hint registration for Ollama integration.