[Bug] Cannot replace worker client if default Runtime is used

Describe the bug

Our check that the runtime is the same on the replaced client as is on the worker does not work if the runtime is not set on the client (i.e. lazily uses the default). We need to either more eagerly set the runtime default on the client config for the service, or use a different way to obtain the runtime of the bridge service client when comparing.

Replication:

import asyncio
from dataclasses import dataclass
from datetime import timedelta

from temporalio import activity, workflow
from temporalio.client import Client
from temporalio.worker import Worker


# While we could use multiple parameters in the activity, Temporal strongly
# encourages using a single dataclass instead which can have fields added to it
# in a backwards-compatible way.
@dataclass
class ComposeGreetingInput:
    greeting: str
    name: str


# Basic activity that logs and does string concatenation
@activity.defn
async def compose_greeting(input: ComposeGreetingInput) -> str:
    activity.logger.info("Running activity with parameter %s" % input)
    return f"{input.greeting}, {input.name}!"


# Basic workflow that logs and invokes an activity
@workflow.defn
class GreetingWorkflow:
    @workflow.run
    async def run(self, name: str) -> str:
        workflow.logger.info("Running workflow with parameter %s" % name)
        return await workflow.execute_activity(
            compose_greeting,
            ComposeGreetingInput("Hello", name),
            start_to_close_timeout=timedelta(seconds=10),
        )


async def main():
    # Uncomment the lines below to see logging output
    # import logging
    # logging.basicConfig(level=logging.INFO)

    # Start client
    client = await Client.connect("localhost:7233")

    client_2 = await Client.connect("localhost:7233")


    # Run a worker for the workflow
    async with Worker(
        client,
        task_queue="hello-activity-task-queue",
        workflows=[GreetingWorkflow],
        activities=[compose_greeting],
    ) as worker:

        worker.client = client_2

        # While the worker is running, use the client to run the workflow and
        # print out its result. Note, in many production setups, the client
        # would be in a completely separate process from the worker.
        result = await client.execute_workflow(
            GreetingWorkflow.run,
            "World",
            id="hello-activity-workflow-id",
            task_queue="hello-activity-task-queue",
        )
        print(f"Result: {result}")


if __name__ == "__main__":
    asyncio.run(main())

In the meantime, simply using default=temporalio.runtime.Runtime.default() in the client connect calls will work around the issue.

Start by running the provided worker-client replacement reproduction and trace the runtime comparison used when assigning worker.client. The work is complete when replacing the client succeeds with the default runtime configuration, while preserving the existing runtime-mismatch check and covering the behavior with a regression test.