DLSS Enabler static-embedding compatibility

[artur-graniszewski]

Summary

Adds the ability to build OptiScaler as a static library and embed it into a
host DLL (e.g. DLSS Enabler), alongside the existing standalone DLL build.
All new behavior is gated behind the OPTISCALER_STATIC macro and a dedicated
build configuration, so the default DLL build path is completely unaffected.

Changes

• New ReleaseStatic build configuration. Builds OptiScaler as a static .lib
  with the static CRT (/MT) and defines OPTISCALER_STATIC. Because the CRT is
  linked statically, any static dependencies it pulls in (e.g. the FSR3 /
  FidelityFX SDK) must be compiled in the same /MT mode — mixing /MT and /MD
  within one module causes CRT symbol conflicts.
• DllMain demotion (static build only). Under OPTISCALER_STATIC, DllMain
  is renamed to org_dllMain via a forced-include macro. It stops being the module
  entry point and becomes a regular function the host can call. In standard DLL
  builds the macro is not defined, so DllMain remains the entry point as before.
• Public embedding API. OptiScaler_Init(HMODULE self, const OptiScalerConfig* cfg)
  and OptiScaler_Shutdown() forward to the original DllMain logic with
  DLL_PROCESS_ATTACH / DLL_PROCESS_DETACH, preserving the existing init and
  cleanup paths. The host passes its own module handle for module-relative lookups.
• OptiScalerConfig struct for future use.
• Duplicate-symbol fixes that surfaced when linking statically alongside the
  host's own version-check code.