perf: Resources::GetDamagetypeImage takes its key by value and looks it up twice #2520

Found by a static pass with the new .agents/skills/performance-audit skill. Not measured.

Resources::GetDamagetypeImage (GWToolboxdll/Modules/Resources.cpp:964):

IDirect3DTexture9** Resources::GetDamagetypeImage(std::string dmg_type)   // by value -> allocation per call
{
    if (damagetype_icons.contains(dmg_type)) {
        return damagetype_icons.at(dmg_type);                             // second lookup on the hit path
    }

It is called per row, per frame from TargetInfoWindow::Draw (Windows/TargetInfoWindow.cpp:471), so the cache-hit path - which is every frame after the first - pays a std::string construction plus two hashed lookups.

Suggested fix: take std::string_view (or const std::string&) and resolve with a single find(). Worth checking the neighbouring Resources::Get*Image accessors for the same shape while in there (GetProfessionImage at Resources.cpp:929 does the same double lookup).