Test coverage - Expand C# SDK test suite

[cloutiertyler]

Definition of Done

• [ ] [UNIT] Test to ensure that one off queries work
• [ ] [INTEGRATION] Test to ensure that one off queries work
• [ ] [INTEGRATION] Test to make sure that you can create a subscription and receive inserts, updates, and deletes
• [ ] [INTEGRATION] Test to see that when you submit a query that violates row limit, you receive an appropriate error and not an exception
• [ ] [INTEGRATION] Test to change your subscription and ensuring that the new data is applied correctly (all old data is deleted and all new data is inserted)
• [ ] [UNIT] Test to ensure that after a message is received on the websocket it takes less than X (reasonable time) to deserialize and populate into the client cache table.

[cloutiertyler]

For integration tests that require testing against SpacetimeDB this repo should assume that SpacetimeDB is running on a standard host and port on the current machine (e.g. localhost:3000)