Ensure envs.integrations can be installed via full path

[mikasenghaas]

Description

This catches a regression in WordleEnv which tries to install from verifiers.envs.integrations.textarena_env import TextArenaEnv but integrations is not exported.

Before

>>> import verifiers.envs.integrations
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ModuleNotFoundError: No module named 'verifiers.envs.integrations'

After

>>> import verifiers.envs.integrations.textarena_env
>>> from verifiers.envs.integrations.textarena_env import TextArenaEnv

This should fix the integration test failing on the hub

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

Exposes verifiers.envs.integrations from the envs package to allow full-path imports used by integration envs.

• Adds from . import integrations as integrations to verifiers/envs/__init__.py, enabling import verifiers.envs.integrations.textarena_env (fixes ModuleNotFoundError).

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