fix: Update throttling logic to use exponential back-off

[zastrowm]

Description

Previous to this change, current_delay was being thrown away and not applied to subsequent retries meaning that we always slept for the same amount of time instead of applying exponential backoff.

Added a test to ensure this going forward.

It looks like this was a bug introduced as part of a previous refactor (a331e63).

Related Issues

N/A

Documentation PR

N/A

Type of Change

Bug fix

Testing

• 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
• Any dependent changes have been merged and published

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