Improve the package quality of copied scan_ground_filter (from autoware.universe) package

[sasakisasaki]

Checklist

• I've read the contribution guidelines.
• I've searched other issues and no duplicate issues were found.
• I've agreed with the maintainers that I can plan this task.

Description

This PR provides a feature that of scan_ground_filter in autoware.universe. But the PR contains files that of just a copy from the autoware.universe side. So, let me plan for refactoring.

Goals of Refactoring

• Improve overall code readability and maintainability.
• Enrich documentation to aid future development and understanding
  • This is also for defining the logic and behavior so all the developers can have the same understanding.
• Validate functionality and performance through systematic testing.

Current Issues

Functional Issues

• Lack of test coverage for certain edge cases.
  • e.g. Empty pointcloud
• Difficult to verify correctness of existing logic due to lack of documentation.
  • e.g. What kind of pointcloud is valid and not for input

Refactoring Actions

• Improve separation of functionalities and modularity.
• Rename variables and functions for easy-to-understand.
• Remove dead code and reduce duplication.

Documentation Improvements

• Create or update the following documentation:
  • Specification: Describe the expected behavior and data flow.
  • Tested Cases: List the scenarios that have been tested.
  • Limitations: Note known limitations and non-supported scenarios.
  • Design Rationale: Explain key architectural decisions, if applicable.

Testing Strategy

• Unit Tests

  • Run all implemented tests in CI as we are doing.

• Real Vehicle Testing

  • Conduct tests in real vehicle conditions.
  • Evaluate and record:
    • Ground removal results
    • Inference time
    • Memory usage
  • Summarize these findings and include them in the final PR.

Purpose

Package quality improvement as above

Possible approaches

Described in "Plan for Refactoring" in "Description" above

Definition of done

All the "Goals of Refactoring" are achieved