fix(bedrock): creating an agent with default parameters successfully in non-US regions

[cerashdan]

Description

Creating a Strands agent with default parameters (default model ID) causes the agent creation to fail in non-US region like eu-central-1 or ap-south-1 due to hardcoded model identitfer DEFAULT_BEDROCK_MODEL_ID = "us.anthropic.claude-sonnet-4-20250514-v1:0" which only works in US based regions.

The current problems is that model selection happens before region resolution. This PR changes this order such that model selection depends on region resolution first, followed by getting the regional cross-region inference model id for the AWS partition where the agent is created (e.g. apac.anthropic.claude-sonnet-4-20250514-v1:0 or eu.anthropic.claude-sonnet-4-20250514-v1:0)

We dynamically resolve the inference profile ID for the resolved region allowing this fix to work in future regions without modification.

Test suite has been updated to cater for these new changes.

Related Issues

#732

Documentation PR

N/A

Type of Change

Bug fix

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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