feat(environment): portable layer states, named views and UCS on both engines

Layer states are ACADMCP_LAYERSTATES XRECORD chunks (<= 255 ASCII chars each),
in the file and not in AutoCAD's Layer States Manager. Headless view restore
writes the *Active VPORT (ezdxf's header has no $VIEWCTR; measured). UCS is
stored and made current; tool coordinates stay WCS.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

engineering/environment/views.py

@@ -0,0 +1,32 @@
+"""Named-view arguments, validated before either engine writes."""
+
+from __future__ import annotations
+
+import math
+
+
+def _finite(value, where: str) -> float:
+    if isinstance(value, bool) or not isinstance(value, (int, float)):
+        raise ValueError(f"{where} must be a number, got {value!r}")
+    number = float(value)
+    if not math.isfinite(number):
+        raise ValueError(f"{where} must be finite")
+    return number
+
+
+def resolve_view_args(center, height, width) -> dict:
+    """``{"center": (x, y) | None, "height": float | None, "width": float | None}``."""
+    out: dict = {"center": None, "height": None, "width": None}
+    if center is not None:
+        if not isinstance(center, (list, tuple)) or len(center) != 2:
+            raise ValueError("center must be an [x, y] pair")
+        out["center"] = (_finite(center[0], "center.x"), _finite(center[1], "center.y"))
+    if height is not None:
+        out["height"] = _finite(height, "height")
+        if out["height"] <= 0:
+            raise ValueError(f"height must be > 0, got {out['height']}")
+    if width is not None:
+        out["width"] = _finite(width, "width")
+        if out["width"] <= 0:
+            raise ValueError(f"width must be > 0, got {out['width']}")
+    return out