ci: disable Nix builder timeout for KVM soaks

[Jesssullivan]

Summary

• disables Nix builder and silent-output timeouts in the shared KVM build wrapper
• adds the shared KVM build wrapper to KVM soak path filters so wrapper changes trigger proof workflows

Evidence

• login-manager persistence failed on main with builder failed due to signal 9 (Killed) while cgroup memory events were oom=0, oom_kill=0, max=0, memory peak was ~14.4GiB under a 64Gi limit, pids were low, and disk had ~267Gi free
• the VM test driver reported Test will time out and terminate in None seconds, so the kill was outside the driver global timeout
• local validation: bash -n .github/scripts/run-kvm-nix-build.sh, git diff --check, workflow YAML parsed with yq, and nix build --option timeout 0 --option max-silent-time 0 --dry-run .#checks.x86_64-linux.rocky-10_1-budgie-graphical-login-manager-persistence-test