Initial support for a multi-task property status database

This adds initial support for an sqlite database that is shared across
multiple tasks of a single SBY file and that can track the status of
individual properties.

The amount of information tracked in the database is currently quite
minimal and depends on the engine and options used. This can be
incrementally extended in the future.

The ways in which the information in the database can be queries is even
more limited for this initial version, consisting of a single '--status'
option which lists all properties and their status.

sbysrc/sby_design.py

@@ -88,6 +88,10 @@ class SbyProperty:
                 return c.FAIR
             raise ValueError("Unknown property type: " + name)
 
+        @property
+        def assume_like(self):
+            return self in [self.ASSUME, self.FAIR]
+
     name: str
     path: Tuple[str, ...]
     type: Type
@@ -171,9 +175,12 @@ class SbyDesign:
     properties_by_path: dict = field(default_factory=dict)
 
     def pass_unknown_asserts(self):
+        updated = []
         for prop in self.hierarchy:
             if prop.type == prop.Type.ASSERT and prop.status == "UNKNOWN":
                 prop.status = "PASS"
+                updated.append(prop)
+        return updated
 
 
 def cell_path(cell):