env worker integration

[mikasenghaas]

Description

this pr enables each env within an env group to have their own env server and handles routing by using the correct env client to send run_rollout and run_group requests.

also includes some minor improvs to logging

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Test improvement

Testing

• All existing tests pass when running uv run pytest locally.
• New tests have been added to cover the changes

Checklist

• My code follows the style guidelines of this project as outlined in AGENTS.md
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Additional Notes

---

Note

Medium Risk
Touches core rollout execution paths and server-mode routing; mis-selection of EnvClient or changed error/log handling could affect remote evaluation behavior across environments.

Overview
Adds per-environment server routing for EnvGroup by overriding run_rollout/run_group to forward requests to the task-specific sub-environment and selecting the most specific EnvClient (env_client arg → sub-env env.env_client → group self.env_client).

Extends Environment.run_rollout/run_group to accept an optional env_client override, enabling callers (including EnvGroup) to direct server-mode execution to a particular remote worker.

Improves server/client operability: start_server now accepts log_file_level (propagated to OpenEnvEnv), ZMQ server logs are promoted to info, and ZMQ client/server logging/error reporting is streamlined (less debug noise; server sends repr(e) and client raises the server-provided error directly).

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