feat: NAPALM drivers for VMware ESXi and vCenter

Two drivers from one package, both in the hypervisor role:

- vmware_esxi talks to one host directly: facts, vmnics and vmkernel
  NICs, CDP/LLDP neighbours, sensors, VMs, datastores and port groups.
- vmware_vcenter talks to a vCenter: every VM of every host it manages,
  with the host as the VM's node, plus distributed port groups. It
  reports no interfaces of its own; the hosts' NICs belong to the hosts.

Both implement the HypervisorDriver VM contract: get_vms, get_vm_config,
start/stop/reboot/suspend_vm and the four snapshot methods, and emit raw
device warnings (maintenance mode, disconnected host, config issues,
host managed by a vCenter, free license making the API read-only).

Every read is a PropertyCollector query for the explicit paths in
paths.py, converted by to_plain() into dicts and lists; the parsers
only ever see that. tools/harvest.py dumps exactly those paths to JSON
and tools/sanitize.py scrubs the dump, so a real host can become a test
fixture without code changes. A VM's vmid is its instance UUID, which
survives vMotion and re-registration; a MoRef does not.

Tested against govmomi's vcsim in ESXi and vCenter mode, including real
power and snapshot tasks. Not yet tested against real hardware.

tests/conftest.py

@@ -0,0 +1,68 @@
+"""Shared fixtures: harvested inventories and a fake Inventory that serves them.
+
+The JSON files under ``fixtures/`` were produced by ``tools/harvest.py``
+against govmomi's vcsim simulator (``vmware/vcsim`` and ``vmware/vcsim -esx``).
+They have the real vSphere shapes but simulator values: vcsim labels devices
+``disk-202-0`` where a real host says ``Hard disk 1``, reports no sensors to
+speak of, and sets ``managementServerIp`` to ``0.0.0.0``. Tests that need a
+branch vcsim does not produce copy a fixture and edit it.
+"""
+
+from __future__ import annotations
+
+import copy
+import json
+from collections.abc import Sequence
+from pathlib import Path
+from typing import Any
+
+import pytest
+
+FIXTURES = Path(__file__).parent / "fixtures"
+_CACHE: dict[str, dict[str, Any]] = {}
+
+
+def load(name: str) -> dict[str, Any]:
+    """A private deep copy of fixture ``name``; tests may mutate it freely."""
+    if name not in _CACHE:
+        _CACHE[name] = json.loads((FIXTURES / f"{name}.json").read_text())
+    return copy.deepcopy(_CACHE[name])
+
+
+class FakeInventory:
+    """Serves a harvest dump the way ``Inventory`` serves a live endpoint."""
+
+    def __init__(self, data: dict[str, Any]) -> None:
+        self.data = data
+        self.calls: list[tuple[str, tuple[str, ...]]] = []
+
+    def about(self) -> dict[str, Any]:
+        return self.data["about"]
+
+    def licenses(self) -> list[dict[str, Any]]:
+        return self.data.get("licenses", [])
+
+    def collect(self, type_name: str, paths: Sequence[str]) -> list[dict[str, Any]]:
+        self.calls.append((type_name, tuple(paths)))
+        rows = self.data["objects"].get(type_name, [])
+        wanted = set(paths) | {"_moref"}
+        return [{k: v for k, v in row.items() if k in wanted} for row in rows]
+
+    # Convenience for tests that tweak a fixture.
+    def objects(self, type_name: str) -> list[dict[str, Any]]:
+        return self.data["objects"][type_name]
+
+
+@pytest.fixture
+def esxi_data() -> dict[str, Any]:
+    return load("vcsim-esxi")
+
+
+@pytest.fixture
+def vcenter_data() -> dict[str, Any]:
+    return load("vcsim-vcenter")
+
+
+@pytest.fixture
+def esxi_host(esxi_data) -> dict[str, Any]:
+    return esxi_data["objects"]["HostSystem"][0]