tests: add tests for crun custom annotations

tests: add tests for crun custom annotations

Add comprehensive tests for crun-specific OCI annotations that were
previously untested:

- run.oci.hooks.stdout/stderr: Test hook output redirection to files
- run.oci.seccomp_fail_unknown_syscall: Test failure on unknown syscalls
- run.oci.systemd.subgroup: Test custom systemd subgroup naming
- run.oci.delegate-cgroup: Test cgroup delegation (cgroup v2 only)
- run.oci.systemd.force_cgroup_v1: Test forcing cgroup v1 on v2 systems
- run.oci.mount_context_type: Test SELinux mount context types
- run.oci.pidfd_receiver: Test pidfd transmission to UNIX socket

All tests include proper skip detection for:
- Nested namespace environments
- Missing root privileges
- Unavailable features (SELinux, systemd, cgroup v2, etc.)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>