Extract OnBeginRequest logic into a testable core layer

[sassi67]

Summary

• Adds src/core, an IIS/Windows-independent static library (IISNativeModuleCore, namespace core) holding the Verdict enum (Continue/Finish mirroring RQ_NOTIFICATION_CONTINUE/RQ_NOTIFICATION_FINISH_REQUEST), the IRequest/IResponse/IContext/IEventProvider/IModule interfaces mirroring their IIS counterparts, and ModuleHandler — which now carries the full OnBeginRequest logic (403 + reason for /forbidden paths, X-IISRequestLevelModule: 1 header otherwise). Nothing in src/core includes Windows or IIS headers; HRESULT-shaped values travel as std::int32_t.
• IISRequestLevelModule becomes a thin adapter: it takes a non-owning core::IModule* via constructor injection, wraps the live IIS objects in the IISContext/IISRequest/IISResponse/IISEventProvider adapters (one file pair per class), delegates, and maps the returned Verdict back to a REQUEST_NOTIFICATION_STATUS. The factory owns the shared stateless ModuleHandler and injects it into every instance it creates.
• Adds test/core/ModuleHandlerTest.cpp: hand-rolled mocks of the core interfaces exercise the real ModuleHandler for the two scenarios from the issue — a /forbidden url (expects Finish, 403, access-denied error on response and provider, no header) and a generic url (expects Continue and the X-IISRequestLevelModule: 1 header).
• Files in src/module, src/core, and test/core are named after the class they hold (PascalCase); register_module.cpp and iis_native_module.def keep their names since they hold no class.

Design decisions (confirmed during implementation)

• IContext declares GetRequest() -> IRequest* / GetResponse() -> IResponse* (the issue text had the names swapped).
• IResponse also declares SetHeader, so ModuleHandler can carry the complete current behavior including the header stamping.
• Tests mock the core interfaces (with the url fed through the mock request's constructor) rather than mocking IModule itself, so the real ModuleHandler logic is what's exercised.

Test plan

• Full build of all 5 targets clean (windows-x86-64-debug), including the new IISNativeModuleCore
• All 3 tests pass: the 2 new TestCore scenarios plus the existing smoke test

Closes #11

🤖 Generated with Claude Code