qemu: add u2fEmuSupport option using libu2f-emu

Adds a u2fEmuSupport flag (default: false) to enable the u2f-emulated
virtual USB device in QEMU, backed by libu2f-emu. This allows NixOS VM
tests to use a software FIDO/U2F token without hardware.

pkgs/by-name/qe/qemu/package.nix

@@ -92,6 +92,8 @@
   fuse3,
   canokeySupport ? false,
   canokey-qemu,
+  u2fEmuSupport ? false,
+  libu2f-emu,
   capstoneSupport ? !minimal,
   capstone,
   valgrindSupport ? false,
@@ -245,6 +247,7 @@ stdenv.mkDerivation (finalAttrs: {
   ++ lib.optionals uringSupport [ liburing ]
   ++ lib.optionals fuseSupport [ fuse3 ]
   ++ lib.optionals canokeySupport [ canokey-qemu ]
+  ++ lib.optionals u2fEmuSupport [ libu2f-emu ]
   ++ lib.optionals capstoneSupport [ capstone ]
   ++ lib.optionals valgrindSupport [ valgrind-light ];
 
@@ -329,6 +332,7 @@ stdenv.mkDerivation (finalAttrs: {
   ++ lib.optional uringSupport "--enable-linux-io-uring"
   ++ lib.optional fuseSupport "--enable-fuse"
   ++ lib.optional canokeySupport "--enable-canokey"
+  ++ lib.optional u2fEmuSupport "--enable-u2f"
   ++ lib.optional capstoneSupport "--enable-capstone"
   ++ lib.optional (!pluginsSupport) "--disable-plugins"
   ++ lib.optional (!enableBlobs) "--disable-install-blobs"