Currently cannot cast from dict to `Model`

[smurf-cm]

Here's some example code to replicate the issue.

from __future__ import annotations
import tinychain as tc 

URI = tc.URI("http://127.0.0.1:8702/demo")


class User(tc.app.Model):
    __uri__ = URI.append("user")

    username = tc.Column("username", tc.String, 100)

    def __init__(self, username):
        self.username = username


class UserService(tc.graph.Graph):
    __uri__ = URI

    @tc.post
    def create_user(self, new_user: User) -> tc.Number:
        user_id = self.user.max_id() + 1
        return tc.After(
            self.user.insert([user_id], [new_user.username]),
            user_id
        )


def start_host(name, apps):
    from tests.tctest.process import start_local_host, start_docker

    # return start_local_host(name, apps)
    return start_docker(name, apps)


if __name__ == "__main__":
    host = start_host("demo", [UserService(models=[User])])
    host.post("/demo/create_user", {"username": "user"})

When running the above we get the following error:

Traceback (most recent call last):
  File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/home/cormac/workspace/python/tinychain/script.py", line 43, in <module>
    assert host.post("/demo/create_user", {"username": "user"}) == 10
  File "/home/cormac/workspace/python/tinychain/client/tinychain/host.py", line 113, in post
    return self._handle(request)
  File "/home/cormac/workspace/python/tinychain/client/tinychain/host.py", line 48, in _handle
    raise BadRequest(response)
tinychain.error.BadRequest: {'/error/bad_request': {'message': 'cannot cast into type String from: (username, /state/scalar/value/string, 100)', 'stack': ['while resolving _return_when', 'in call to POST class http://127.0.0.1:8702/demo instance /create_user']}}