Support the Windows CMake build for the mimalloc redirect

[Grantim]

Summary

• Add cmake/Modules/MimallocRedirect.cmake with mr_enable_mimalloc_redirect(target): on Windows it find_package(mimalloc), links the imported target, and forces /INCLUDE:mi_version so mimalloc.dll loads early enough for mimalloc-redirect.dll to take over the CRT allocator process-wide. No-op on other platforms (Emscripten already links mimalloc via -sMALLOC=mimalloc).
• Apply it to MeshViewer and MRTest, so the Windows CMake build gets the redirect — previously only the MSBuild/.vcxproj path had it.
• Drop the hardcoded mimalloc import-lib name from MRViewerApp.vcxproj / MRTest.vcxproj. The name differs across versions (2.x mimalloc.lib, 3.x mimalloc.dll.lib); vcpkg's lib\*.lib auto-link plus the mi_version anchor already pull it in, so naming it explicitly only risked LNK1181 on toolchains resolving a different mimalloc version.

Test plan

• Windows CMake build of MeshViewer/MRTest links and runs.
• Windows MSBuild build links (no LNK1181).
• mi_is_redirected() returns 1 at runtime.
• Non-Windows CMake builds unaffected (helper is a no-op).

[oitel]

The comments are now obsolete, I believe.

[oitel]

The comments are now obsolete, I believe.

[oitel]

The function name is confusing since it, in fact, doesn't enable anything on any platform other than Windows. I suggest renaming it to mr_win32_enable_mimalloc_redirect and putting the WIN32 check before its calls explicitly, like:

if(WIN32)
  include(MimallocRedirect)
  mr_win32_enable_mimalloc_redirect(${PROJECT_NAME})
endif()

[Grantim]

Thanks @oitel — both addressed in 3836d62:

• Helper naming + guard. Renamed mr_enable_mimalloc_redirect → mr_win32_enable_mimalloc_redirect and moved the if(WIN32) check to the call sites (so the module is only included on Windows and the helper no longer silently no-ops elsewhere), as you suggested.
• .vcxproj comments. Dropped the obsolete part — the import-lib naming / version rationale only mattered while we still named the lib explicitly. I kept a single one-line note on why mi_version is force-referenced (it's the anchor that makes mimalloc.dll load so mimalloc-redirect.dll can take over the allocator), since that intent isn't obvious from a bare <ForceSymbolReferences>. Happy to drop it entirely if you'd prefer.