feat(openstack-sync): create subnet pools and their address scopes

[haseebsyed12]

What does this change do?

• Each NeutronSubnetPool CR creates one Neutron subnet pool; CIDRs come from Nautobot prefixes referenced by UUID, pool policy (name, address scope, prefix bounds, sharing) lives on the CR.
• Subnet-pool sync creates the address scope if absent, adopts it if present, and never deletes it (scopes have no ownership marker and outlive any pool).
• Nautobot stays CIDRs-only; pool policy lives on the CR.

Upgrade impact

• This change requires operator action to upgrade. If checked, add the
  upgrade-impact label and a release note: run scriv create from the
  repository root and describe the required action in the generated
  changelog.d/ file. See RELEASING.md.

Operator action means anything a deployment has to do beyond a normal resync:
deploy repo or values changes, new or removed secrets, enabling or disabling a
component, or a manual one-time step.

[github-actions]

Python test results

129 tests  +53   129 ✅ +53   12s ⏱️ +8s
  1 suites ± 0     0 💤 ± 0 
  1 files   ± 0     0 ❌ ± 0 

Results for commit 19f47aa. ± Comparison against base commit 1ff4506.

This pull request removes 76 and adds 129 tests. Note that renamed tests count towards both.

ironic_understack.tests.test_device_type ‑ test_device_type_from_directory
ironic_understack.tests.test_device_type ‑ test_device_type_from_yaml
ironic_understack.tests.test_device_type ‑ test_device_type_minimal_yaml
ironic_understack.tests.test_device_type ‑ test_get_resource_class
ironic_understack.tests.test_inspect_hook_chassis_model ‑ test_preserves_other_custom_traits
ironic_understack.tests.test_inspect_hook_chassis_model ‑ test_replaces_stale_chassis_trait
ironic_understack.tests.test_inspect_hook_node_name_check.TestInspectHookNodeNameCheck ‑ test_empty_system_vendor
ironic_understack.tests.test_inspect_hook_node_name_check.TestInspectHookNodeNameCheck ‑ test_matching_name_passes
ironic_understack.tests.test_inspect_hook_node_name_check.TestInspectHookNodeNameCheck ‑ test_mismatched_name_raises
ironic_understack.tests.test_inspect_hook_node_name_check.TestInspectHookNodeNameCheck ‑ test_missing_manufacturer_raises
…

tests.test_backup ‑ test_local_backs_up_mariadb_and_both_ovn_dbs
tests.test_backup ‑ test_local_mariadb_expands_password_inside_pod_not_locally
tests.test_backup ‑ test_local_ovn_uses_ovsdb_container_and_socket_paths
tests.test_backup ‑ test_local_skip_both_is_an_error
tests.test_backup ‑ test_local_surfaces_backup_exec_error
tests.test_backup ‑ test_slug_sanitizes_non_alnum
tests.test_cli ‑ test_bare_invocation_shows_usage_instead_of_missing_command_error
tests.test_cli ‑ test_bare_net_shows_usage_instead_of_missing_command_error
tests.test_cli ‑ test_bare_router_shows_usage_instead_of_missing_command_error
tests.test_cli ‑ test_callback_builds_connection_context
…

♻️ This comment has been updated with latest results.

[geetikabatra]

LGTM