Make object handling happen at the world level, fix region handoffs

The previous model didn't really map to how Indra handles objects:
In Indra Local IDs are only really used to look up the FullID, and
that's used to look at a global object list.

This moves to a model where the world (Session) owns the object, and
objects can be freely moved between regions without killing the world's
reference to it.

The two ID design for objects was a mistake in my opinion, but whatever.

tests/proxy/test_httpflows.py

@@ -1,27 +1,14 @@
-import unittest
-
 from mitmproxy.test import tflow, tutils
 
-from hippolyzer.lib.base.datatypes import UUID
 from hippolyzer.lib.proxy.http_flow import HippoHTTPFlow
 from hippolyzer.lib.proxy.message_logger import HTTPMessageLogEntry
-from hippolyzer.lib.proxy.sessions import SessionManager
+
+from . import BaseProxyTest
 
 
-class TestHTTPFlows(unittest.TestCase):
+class TestHTTPFlows(BaseProxyTest):
     def setUp(self) -> None:
-        self.session_manager = SessionManager()
-        self.session = self.session = self.session_manager.create_session({
-            "session_id": UUID.random(),
-            "secure_session_id": UUID.random(),
-            "agent_id": UUID.random(),
-            "circuit_code": 0,
-            "sim_ip": "127.0.0.1",
-            "region_x": 1,
-            "region_y": 2,
-            "sim_port": "1",
-            "seed_capability": "https://test.localhost:4/foo",
-        })
+        super().setUp()
         self.region = self.session.register_region(
             ("127.0.0.1", 2),
             "https://test.localhost:4/foo",