test: drop imports orphaned by the MockClient consolidation

Removing the three local mock classes left their type-only imports
(AsyncIterator, LLMResponse, ChunkType, StreamChunk, ToolSpec) unused;
drop the ones no longer referenced.

Author: SuperMarioYL

tests/unit/test_eval_budget.py

@@ -2,15 +2,13 @@
 
 from __future__ import annotations
 
-from collections.abc import AsyncIterator
 from functools import partial
 from typing import Any
 
 import pytest
 
-from forge.clients.base import ChunkType, StreamChunk
 from forge.context.strategies import TieredCompact
-from forge.core.workflow import LLMResponse, ToolCall, ToolSpec, TextResponse
+from forge.core.workflow import ToolCall, TextResponse
 
 from tests.conftest import MockClient
 from tests.eval.eval_runner import EvalConfig, RunResult, run_scenario

tests/unit/test_runner.py

@@ -3,7 +3,6 @@
 from __future__ import annotations
 
 import asyncio
-from collections.abc import AsyncIterator
 from unittest.mock import MagicMock
 
 import pytest
@@ -15,7 +14,6 @@
 from forge.core.runner import WorkflowRunner
 from pydantic import BaseModel
 from forge.core.workflow import (
-    LLMResponse,
     TextResponse,
     ToolCall,
     ToolDef,