fix(bedrock): preserve aws_profile in copied clients

[pragnyanramtha]

Summary

• preserve aws_profile when copying sync and async Bedrock clients
• allow copy()/with_options() callers to override aws_profile explicitly
• add regression coverage for sync preserve, sync override, and async preserve cases

Why

A Bedrock client configured with aws_profile would lose that profile after copy()/with_options(). The copied client still preserved region and other credential options, but request signing would use aws_profile=None and could fall back to the default AWS profile.

Tests

• uv run --frozen --extra bedrock pytest tests/lib/test_bedrock.py -q
• uv run --frozen ruff check src/anthropic/lib/bedrock/_client.py tests/lib/test_bedrock.py
• uv run --frozen ruff format --check src/anthropic/lib/bedrock/_client.py tests/lib/test_bedrock.py
• git diff --check

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