Enable .NET functions in check-pr for Agent-specific functions (#2119)

Enable the .NET functions for the agent by sending the agent the URI for the `-net` service.

Also fix some things causing failures when using the .NET functions (`CouldShrinkScaleset` was not implemented).

Improve error handling around table serialization/deserialization, fix an issue with int64/long mismatch between Python & C# code.

----

For `check-pr` testing:

1. There's a new parameter `enable_dotnet` which maps directly to the `--enable_dotnet` switch on `deploy.py`.
2. If you put `agent` there, all the `agent_*` functions will be enabled for .NET and disabled for Python.
3. If `agent_can_schedule` is disabled on the Python side, it will automatically tell the agent to use the .NET functions.

So to test the .NET agent functions, do a `check-pr` run with `enable_dotnet` set to `agent` and it should all work.

src/api-service/__app__/onefuzzlib/extension.py

@@ -24,7 +24,7 @@ from .azure.containers import (
     get_file_url,
     save_blob,
 )
-from .azure.creds import get_instance_id, get_instance_url
+from .azure.creds import get_agent_instance_url, get_instance_id
 from .azure.log_analytics import get_monitor_settings
 from .azure.queue import get_queue_sas
 from .azure.storage import StorageType
@@ -246,7 +246,7 @@ def build_scaleset_script(pool: Pool, scaleset: Scaleset) -> str:
 def build_pool_config(pool: Pool) -> str:
     config = AgentConfig(
         pool_name=pool.name,
-        onefuzz_url=get_instance_url(),
+        onefuzz_url=get_agent_instance_url(),
         heartbeat_queue=get_queue_sas(
             "node-heartbeat",
             StorageType.config,