evaluation/__init__.py unconditionally imports optional strands dependencies

[jariy17]

Bug

src/bedrock_agentcore/evaluation/__init__.py unconditionally imports from strands_agents_evals and span_to_adot_serializer:

from bedrock_agentcore.evaluation.integrations.strands_agents_evals.evaluator import (
    StrandsEvalsAgentCoreEvaluator,
    create_strands_evaluator,
)
from bedrock_agentcore.evaluation.span_to_adot_serializer import (
    convert_strands_to_adot,
)

However, strands-agents and strands-agents-evals are declared as optional dependencies in pyproject.toml:

[project.optional-dependencies]
strands-agents = ["strands-agents>=1.1.0"]
strands-agents-evals = ["strands-agents-evals>=0.1.0"]

This causes an ImportError when a user installs bedrock-agentcore without the strands extras and tries to use EvaluationRunner or EvaluationClient:

from bedrock_agentcore.evaluation import EvaluationRunner
  -> ImportError (strands_agents_evals not installed)