Update the test_policy integration test to work with new PolicyEngine service.

[pradeepfn]

This PR trying to solve two challenges;

1. Update the integration test code to work with new policy service API. In the new API, during service init 'setUp' gets called internally. If we call setup again in our test/driver code, it will complain of GPU memory not enough. This is fixed in this PR.

2. With new APIs, we have to send the torchstore references to vllm workers via Policy service. I attempted to pass torchstore references via WorkerConfig (shown in this PR). However, I'm encountering pickling issues. Sending the code to get some feedback from the experts.

Aggregated Logs (2025-09-02 06:35:21) >>>
[1 similar log lines] MAST is not supported on this platform. You can ignore this if you do not work at Meta.
[1 similar log lines] Failed to initialize replica 0: cannot pickle 'monarch._rust_bindings.monarch_hyperactor.mailbox.Mailbox' object
[1 similar log lines] CRITICAL:root:Unhandled exception in actor endpoint
[2 similar log lines] Traceback (most recent call last):
[4 similar log lines] File "/home/pradeepfdo/.conda/envs/forge/lib/python3.10/site-packages/monarch/_src/actor/actor_mesh.py", line 827, in instrumented
[2 similar log lines] result = await the_method(args, **kwargs)
[4 similar log lines] File "/home/pradeepfdo/forge_fork/src/forge/controller/service/service.py", line 115, in initialize
[2 similar log lines] await asyncio.gather([r.initialize() for r in replicas])
[2 similar log lines] self.actor = await self.actor_def.launch(
[2 similar log lines] File "/home/pradeepfdo/forge_fork/src/forge/actors/policy.py", line 131, in launch
[2 similar log lines] "vllm_worker", PolicyWorker, **asdict(config.worker_params)
[6 similar log lines] File "/home/pradeepfdo/.conda/envs/forge/lib/python3.10/dataclasses.py", line 1238, in asdict
[2 similar log lines] return _asdict_inner(obj, dict_factory)
[2 similar log lines] value = _asdict_inner(getattr(obj, f.name), dict_factory)
[2 similar log lines] return copy.deepcopy(obj)
[16 similar log lines] File "/home/pradeepfdo/.conda/envs/forge/lib/python3.10/copy.py", line 172, in deepcopy
[4 similar log lines] y = _reconstruct(x, memo, *rv)
[2 similar log lines] state = deepcopy(state, memo)
[2 similar log lines] y = copier(x, memo)
[2 similar log lines] y[deepcopy(key, memo)] = deepcopy(value, memo)
[2 similar log lines] y = func(*args)
[2 similar log lines] args = (deepcopy(arg, memo) for arg in args)
[2 similar log lines] rv = reductor(4)
[2 similar log lines] TypeError: cannot pickle 'monarch._rust_bindings.monarch_hyperactor.mailbox.Mailbox' object
[1 similar log lines] result = await instrumented()
[1 similar log lines] raise e
<<< Aggregated Logs (2025-09-02 06:35:24) <<<

[pradeepfn]

passing torchstore reference results in pickling errors. Pasted in the summary.

[pradeepfn]

use #115