controller/vm: fix CI failures in mock generation

- Use 'go tool mockgen' instead of bare 'mockgen' in go:generate directives
  (matches go.mod tool directive, ensures CI uses pinned version)
- Add -build_constraint=windows to vmcontroller mock (imports Windows-only packages)
- Remove stale internal/controller/vm/mock/ directory (tests use internal/test/mock/vmcontroller/)

Signed-off-by: Shreyansh Sancheti <shreyanshjain7174@gmail.com>
Signed-off-by: Shreyansh Sancheti <shsancheti@microsoft.com>

Author: Shreyansh Sancheti

internal/controller/vm/interface.go

@@ -2,7 +2,7 @@
 
 package vm
 
-//go:generate mockgen -source=interface.go -package=mock -destination=mock/mock_interface.go
+//go:generate go tool mockgen -source=interface.go -build_constraint=windows -package=mockvmcontroller -destination=../../test/mock/vmcontroller/mock_interface.go
 
 import (
 	"context"