Initial public release — aci-sim v0.16.0

aci-sim is a stateful REST simulator of a 2-site Cisco ACI fabric
(per-site APIC + ND/NDO management planes) — for testing ACI automation
(Ansible cisco.aci / cisco.mso, aci-py, custom REST clients) and CI gates
without real hardware.

Highlights: APIC + NDO REST surface served from one in-memory MIT built
from a declarative topology.yaml; port mode + sandbox (real per-device IPs
on :443) run modes; LLDP/CDP neighbor visibility; NDO->APIC deploy mirror
(multi-site templates materialize onto the target sites' APIC stores);
real-APIC fvBD default attributes; file-backed state save/restore; an
`aci-sim` CLI (validate/show/graph/run/new/init/lldp); and an 888-test suite.

History squashed for the public release.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

aci_sim/topology/loader.py

@@ -0,0 +1,47 @@
+"""Topology YAML loader.
+
+Usage::
+
+    from aci_sim.topology.loader import load_topology
+    topo = load_topology("topology.yaml")
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Union
+
+import yaml
+
+from .schema import Topology
+
+
+def load_topology(path: Union[str, Path]) -> Topology:
+    """Read *path*, parse YAML, validate, and return a :class:`~schema.Topology`.
+
+    Raises
+    ------
+    FileNotFoundError
+        If *path* does not exist.
+    ValueError
+        If the YAML is syntactically invalid.
+    pydantic.ValidationError
+        If the topology fails schema or cross-reference validation; the error
+        message lists every violation found.
+    """
+    path = Path(path)
+    if not path.exists():
+        raise FileNotFoundError(f"Topology file not found: {path}")
+
+    try:
+        raw = yaml.safe_load(path.read_text(encoding="utf-8"))
+    except yaml.YAMLError as exc:
+        raise ValueError(f"Failed to parse YAML from {path}: {exc}") from exc
+
+    if not isinstance(raw, dict):
+        raise ValueError(
+            f"Topology YAML must be a mapping at the top level, got {type(raw).__name__}"
+        )
+
+    # Let ValidationError propagate naturally — callers inspect it directly.
+    return Topology.model_validate(raw)