Add verifiers integration bridge

[kkudumu]

Summary

Adds an optional art.verifiers bridge for Prime Intellect verifiers environments:

• run a verifiers.Environment with an ART model and return an art.Trajectory
• run grouped verifiers rollouts and return an art.TrajectoryGroup
• convert serialized verifiers rollout outputs to ART trajectories
• convert ART trajectories/groups back into verifiers-compatible rollout output dicts
• document the integration under docs/integrations/verifiers-integration.mdx

This is aimed at the ART <-> verifiers portability path from the Algora ART-E / ART bounty without adding verifiers as a hard dependency for normal ART users.

Tests

• python3 -m py_compile src/art/verifiers.py src/art/test/test_verifiers_bridge.py
• PYTHONPATH=/tmp/art-verifiers-test-deps:src pytest -q src/art/test/test_verifiers_bridge.py
• PYTHONPATH=/tmp/art-verifiers-test-deps:src python3 -m ruff check src/art/verifiers.py src/art/test/test_verifiers_bridge.py

[kkudumu]

@algora-pbc This PR targets the Prime Intellect ART-E / ART bounty, specifically the hard-path ART <-> verifiers task portability scope: https://algora.io/PrimeIntellect-ai/bounties/cxptwFoEv2up9Qjm

[kkudumu]

Follow-up pushed:

• expanded tests from 4 to 7, including async wrapper coverage for running single and grouped verifiers environment rollouts with an ART model client
• kept the runtime import optional so base ART installs are unaffected

Verification after the update:

• python3 -m py_compile src/art/verifiers.py src/art/test/test_verifiers_bridge.py
• PYTHONPATH=/tmp/art-verifiers-test-deps:src pytest -q src/art/test/test_verifiers_bridge.py -> 7 passed
• PYTHONPATH=/tmp/art-verifiers-test-deps:src python3 -m ruff check src/art/verifiers.py src/art/test/test_verifiers_bridge.py -> passed

[kkudumu]

Small CI-risk cleanup pushed after the test expansion:

• removed the proposed pyproject.toml optional extra because this repo uses a frozen uv.lock; refreshing the lock in this environment is currently blocked by an existing Megatron build-metadata issue unrelated to this PR
• kept verifiers as an optional runtime import and documented installation as uv pip install -U openpipe-art verifiers
• retained the expanded async wrapper tests

Verification on the updated head:

• python3 -m py_compile src/art/verifiers.py src/art/test/test_verifiers_bridge.py
• PYTHONPATH=/tmp/art-verifiers-test-deps:src pytest -q src/art/test/test_verifiers_bridge.py -> 7 passed
• PYTHONPATH=/tmp/art-verifiers-test-deps:src python3 -m ruff check src/art/verifiers.py src/art/test/test_verifiers_bridge.py -> passed
• git diff --check HEAD -> passed

[kkudumu]

@dhruvrnaik quick visibility note for the Algora ART-E / ART bounty: this PR targets the hard-scope ART <-> verifiers portability path, not just the local ART-E example path.

Current verification on this PR:

• python3 -m py_compile src/art/verifiers.py src/art/test/test_verifiers_bridge.py
• PYTHONPATH=/tmp/art-verifiers-test-deps:src pytest -q src/art/test/test_verifiers_bridge.py -> 7 passed
• PYTHONPATH=/tmp/art-verifiers-test-deps:src python3 -m ruff check src/art/verifiers.py src/art/test/test_verifiers_bridge.py -> passed
• git diff --check HEAD -> passed

The integration keeps verifiers optional, so normal ART installs are unaffected while users who install verifiers get the bridge APIs.

[kkudumu]

Follow-up pushed in 28e59c7 to make the hard-scope 2-way portability contract more explicit.

What changed:

• Added normalize_verifiers_rollout_output() and normalize_verifiers_rollout_outputs().
• These round-trip saved verifiers outputs through ART trajectories and back into verifiers-compatible output shape.
• The normalizer preserves prompt/completion message shape, reward, numeric metrics, tool definitions, logs, completion/truncation state, timing, answer, and stop-condition metadata while carrying ART metadata in the optional trajectory column.
• Added round-trip tests and docs showing the portability check.

Verification rerun:

• python3 -m py_compile src/art/verifiers.py src/art/test/test_verifiers_bridge.py
• PYTHONPATH=/tmp/art-verifiers-test-deps:src pytest -q src/art/test/test_verifiers_bridge.py -> 9 passed
• PYTHONPATH=/tmp/art-verifiers-test-deps:src python3 -m ruff check src/art/verifiers.py src/art/test/test_verifiers_bridge.py -> passed
• git diff --check -> passed