chore: moved truncation logic to conversation manager and added should_truncate_results

[poshinchen]

Description

1. Moved the truncation logic conversation manager.
2. Allow users to disable truncating the tool result with should_truncate_results flag (Default: True).

The behavior of the reduce_context will be:

1. When ContextWindowOverflowException is first thrown, if should_truncate_results is not explicitly set to False, the tool result will get truncated first and execute the event loop again.
2. When ContextWindowOverflowException is thrown again after the truncation, the message history starts to get reduced
3. Successfully execute the event loop / throw ContextWindowOverflowException if nothing can be reduced by conversation manager

Related Issues

#152
#167

Documentation PR

• Context Management
• docs: update context management doc with should_truncate_results flag docs#88

Will update the documentation as follow up.

Type of Change

• Bug fix

Testing

[How have you tested the change?]

• hatch fmt --linter
• hatch fmt --formatter
• hatch test --all
• Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

Checklist

• I have read the CONTRIBUTING document
• I have added 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
• My changes generate no new warnings
• [NA] Any dependent changes have been merged and published

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.