feat: allow programmatic defaults in lightning_cli

[ultmaster]

Summary

• allow passing defaults for lightning_cli arguments
• support programmatic defaults overriding required CLI args
• test default overrides for required parameters

Testing

• pytest

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https://chatgpt.com/codex/tasks/task_e_689590e72300832e95482ca7a6b7e4f8

[Copilot]

Pull Request Overview

This PR enhances the lightning_cli function to accept programmatic defaults that can override required CLI arguments, allowing more flexible configuration management.

Key changes:

• Added a defaults parameter to lightning_cli function for providing programmatic defaults
• Modified argument parsing logic to prioritize programmatic defaults over required argument validation
• Added comprehensive test coverage for the new default override functionality

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
agentlightning/config.py	Adds defaults parameter support throughout the CLI parsing pipeline with proper type annotations and overloads
tests/test_config.py	Extends test helper and adds test cases for programmatic defaults overriding required parameters

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[Copilot]

The condition provided_defaults and param_name in provided_defaults is duplicated from lines 257-258. Consider extracting this logic into a variable to avoid repetition and improve maintainability.

Suggested change

	default_override if provided_defaults and param_name in provided_defaults else _DEFAULT_SENTINEL,
	default_override if has_default_override else _DEFAULT_SENTINEL,