feat: ip_version option to restrict inventories to ipv4 or ipv6

inventory.ip_version (or NETBOX_INVENTORY_IP_VERSION): both (default),
v4 or v6; the ip-addresses source filters by family server-side, the
virtual-machines source picks primary_ip4/primary_ip6 for ansible_host.

tests/test_inventory.py

@@ -91,6 +91,14 @@ class TestValidateOptions:
     def test_named_without_value_is_fine(self):
         inv.validate_options("ip-addresses", "named", "")
 
+    def test_valid_ip_versions_pass(self):
+        for ip_version in ("both", "v4", "v6"):
+            inv.validate_options("ip-addresses", "", "", ip_version)
+
+    def test_unknown_ip_version(self):
+        with pytest.raises(inv.InventoryError, match="Unknown ip_version"):
+            inv.validate_options("ip-addresses", "", "", "ipv4")
+
 
 class TestHostEntries:
     def test_ip_with_dns_name(self):
@@ -133,6 +141,21 @@ class TestHostEntries:
         _, host = inv.vm_host_entry({"name": "vm02"})
         assert "ansible_host" not in host
 
+    def test_vm_ip_version_selects_primary_ip_field(self):
+        vm = {
+            "name": "vm01",
+            "primary_ip": {"address": "2001:db8::20/64"},
+            "primary_ip4": {"address": "192.0.2.20/24"},
+            "primary_ip6": {"address": "2001:db8::20/64"},
+        }
+        assert inv.vm_host_entry(vm, "both")[1]["ansible_host"] == "2001:db8::20"
+        assert inv.vm_host_entry(vm, "v4")[1]["ansible_host"] == "192.0.2.20"
+        assert inv.vm_host_entry(vm, "v6")[1]["ansible_host"] == "2001:db8::20"
+
+    def test_vm_without_requested_family_has_no_ansible_host(self):
+        vm = {"name": "vm01", "primary_ip4": {"address": "192.0.2.20/24"}}
+        assert "ansible_host" not in inv.vm_host_entry(vm, "v6")[1]
+
 
 class TestClientSideFilters:
     def entries(self):
@@ -202,6 +225,15 @@ class TestLoadConfig:
         with pytest.raises(inv.InventoryError, match="url and token"):
             inv.load_config(path)
 
+    def test_ip_version_defaults_to_both(self, tmp_path):
+        path = self.write_config(tmp_path, "netbox:\n  url: https://nb.example.com\n  token: abc\n")
+        assert inv.load_config(path)["ip_version"] == "both"
+
+    def test_ip_version_env_override_is_normalised(self, tmp_path, monkeypatch):
+        path = self.write_config(tmp_path, "netbox:\n  url: https://nb.example.com\n  token: abc\n")
+        monkeypatch.setenv("NETBOX_INVENTORY_IP_VERSION", " V4 ")
+        assert inv.load_config(path)["ip_version"] == "v4"
+
     def test_invalid_timeout_raises(self, tmp_path):
         path = self.write_config(
             tmp_path,
@@ -291,6 +323,20 @@ class TestBuildInventory:
         inventory = inv.build_inventory(config, make_client())
         assert inventory["netbox"]["hosts"] == ["192.0.2.11", "web.example.com"]
 
+    @responses.activate
+    def test_ip_version_becomes_family_parameter(self):
+        responses.get(
+            f"{NETBOX_URL}/api/ipam/ip-addresses/",
+            json={
+                "next": None,
+                "results": [{"address": "2001:db8::10/64", "dns_name": "v6.example.com"}],
+            },
+        )
+        config = {"source": "ip-addresses", "filter": "", "filter_value": "", "ip_version": "v6"}
+        inventory = inv.build_inventory(config, make_client())
+        assert inventory["netbox"]["hosts"] == ["v6.example.com"]
+        assert "family=6" in responses.calls[0].request.url
+
     @responses.activate
     def test_vm_inventory_with_cluster_filter(self):
         responses.get(