step 2: add thread safe state commands and cache model

src/dpg_map/exceptions.py

@@ -27,3 +27,23 @@ class InvalidProviderError(ProviderError, ValueError):
 
 class ProjectionError(DpgMapError, ValueError):
     """Raised when geographic projection input is invalid."""
+
+
+class MapNotFoundError(DpgMapError, KeyError):
+    """Raised when a requested map tag is not registered."""
+
+
+class OverlayNotFoundError(DpgMapError, KeyError):
+    """Raised when a requested overlay tag is not registered."""
+
+
+class CoordinateError(DpgMapError, ValueError):
+    """Raised when geographic coordinate input is invalid."""
+
+
+class ThreadingError(DpgMapError):
+    """Raised when an operation violates dpg-map threading rules."""
+
+
+class CacheError(DpgMapError):
+    """Raised when cache metadata or paths cannot be handled."""