Tune Firecracker machine configuration: vCPU count, memory size, SMT, dirty-page tracking, and huge pages

Documented steps

1. Read the current configuration: `curl --unix-socket /tmp/firecracker.socket -X GET http://localhost/machine-config`.
2. Fully (re)configure with PUT — pre-boot only: `curl --unix-socket /tmp/firecracker.socket -X PUT --data '{"vcpu_count": 2, "mem_size_mib": 1024, "smt": false, "track_dirty_pages": false}' http://localhost/machine-config`.
3. PUT is not a merge: any optional field you omit resets to its default (smt=false, track_dirty_pages=false, cpu_template=None, huge_pages=None).
4. To change one field without resetting others use PATCH (also pre-boot only): `curl --unix-socket /tmp/firecracker.socket -X PATCH --data '{"vcpu_count": 4}' http://localhost/machine-config`.
5. Respect vcpu_count constraints: integer in [1, 32]; with "smt": true it must be 1 or an even number.
6. smt (default false) can only be enabled on x86. track_dirty_pages (default false) enables incremental/diff memory snapshots instead of full-copy-only.
7. huge_pages options: "None" (default, 4K pages), "Transparent" (THP via madvise MADV_HUGEPAGE), "2M" (explicit hugetlbfs 2MB pages — mem_size_mib must then be a multiple of 2).
8. Official doc (MachineConfiguration + /machine-config): https://github.com/firecracker-microvm/firecracker/blob/main/src/firecracker/swagger/firecracker.yaml