fix(bedrock): pass aws_profile to _infer_region() for correct region detection

[Oxygen56]

Summary

When aws_profile is specified in AnthropicBedrock or AnthropicBedrockClient but AWS_REGION is not set, _infer_region() previously created a boto3.Session() without profile_name, defaulting to the 'default' profile and ignoring the caller's explicitly configured profile. This caused cross-region inference failures (HTTP 403) for users with non-default AWS profiles.

Root cause

_infer_region() called boto3.Session() with no arguments, which uses the default profile regardless of what aws_profile the caller specified. The user's profile might have region = us-west-2 configured, but _infer_region would still return us-east-1.

Fix

• Accept an optional aws_profile parameter in _infer_region()
• Pass it through to boto3.Session(profile_name=aws_profile)
• Update both call sites (AnthropicBedrock and AnthropicBedrockClient) to pass aws_profile

Test plan

The fix matches the verified solution from the issue thread (multiple users confirmed it works).

Before:

# profile "prod" has region = us-west-2, but AWS_REGION is unset
client = AnthropicBedrock(aws_profile="prod")
print(client.aws_region)  # us-east-1 (WRONG)

After:

client = AnthropicBedrock(aws_profile="prod")
print(client.aws_region)  # us-west-2 (CORRECT)

Closes #892.