fix: make LLMDescriptionScorer work inside a running event loop

[kayaal34]

Closes #353 (the LLMDescriptionScorer part. TypeSafeDescriptionScorer isn't on dev yet).

Problem

• _init_event_loop took the loop from asyncio.get_event_loop(). When predict() is called from async code (a notebook, a FastAPI handler), that returns the running loop, and run_until_complete raises RuntimeError: This event loop is already running.
• On Python 3.14 get_event_loop() raises when no loop is set, so every instance fell back to new_event_loop(), and clear_cache removed it with delattr without closing it: one leaked loop per HPO trial.

Fix

• Each scorer owns a private loop (asyncio.new_event_loop()) and never touches the caller's loop. I kept one loop per instance on purpose rather than calling asyncio.run per batch: the generator's AsyncOpenAI client pools connections bound to the loop they were opened on, so running every batch on the same loop keeps that pool valid.
• _run_async(coro): with no running loop in the current thread, it runs the batch directly on the scorer's loop. Inside a running loop, it runs the batch on a one-off worker thread and blocks until it finishes. predict() stays synchronous.
• The loop is closed on refit (_init_event_loop) and in clear_cache.

Tests

• test_description_scorer_llm_predict_inside_running_loop: predict() called from a coroutine returns the same result as the sync call, and the scorer still works from sync code afterwards.
• test_description_scorer_llm_closes_its_event_loop: refit and clear_cache close the loop.
• Both new tests fail on dev and pass with this change. tests/modules and tests/pipeline filtered to description/LLM: 24 passed. ruff and mypy on the changed files pass.

This change touches the same lines as #361, so whichever merges second will need a one-line conflict resolved. I can rebase if needed.

[Copilot]

Copilot review overview

🟡 Changes recommended

Unresolved event-loop thread-safety, concurrency, and lifecycle concerns remain.

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Review effort: Lite
Findings: 1

Open (1)

• Prevent cross-thread event loop use and concurrent run_until_complete calls · New

What changed in this PR

Updates LLMDescriptionScorer to support synchronous prediction from running asyncio loops and manage private event-loop cleanup.

Changes:

• Adds worker-thread execution for running-loop callers.
• Closes loops during refit and cache clearing.
• Adds regression tests for async prediction and loop closure.

File	Summary
tests/​modules/​scoring/​test_description_llm.py	Tests running-loop prediction and loop closure.
src/​autointent/​modules/​scoring/​_description/​llm_encoder.py	Implements private loop management and worker-thread execution.

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