test: ensure pytest can import src package

Author: Copilot

tests/conftest.py

@@ -2,8 +2,13 @@
 
 from __future__ import annotations
 
+import sys
+from pathlib import Path
+
 import pytest
 
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+
 from src.client import CompletionResult
 from src.config import EvalConfig, EndpointConfig, PricingConfig