feat: support datafusion iceberg transform physical expr

[xxhZs]

support datafusion iceberg transform physical expr
and mv all datafusion impl to new dir

This is for implementing repartitioning, which is part of #20.

[Copilot]

Pull Request Overview

This PR refactors existing DataFusion executors into a new datafusion_impl directory and adds support for Iceberg column transform expressions in physical plans.

• Moved file_scan_task_table_provider and iceberg_file_task_scan modules under datafusion_impl
• Updated import paths in datafusion_processor and iceberg_file_task_scan
• Introduced IcebergTransformPhysicalExpr to evaluate Iceberg Transform functions in DataFusion

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
core/src/executor/datafusion/mod.rs	Replaced direct module declarations with pub mod datafusion_impl
core/src/executor/datafusion/datafusion_processor.rs	Updated import path for IcebergFileScanTaskTableProvider
core/src/executor/datafusion/datafusion_impl/mod.rs	Added new datafusion_impl module
core/src/executor/datafusion/datafusion_impl/iceberg_physical_expr.rs	Added IcebergTransformPhysicalExpr implementation and tests
core/src/executor/datafusion/datafusion_impl/iceberg_file_task_scan.rs	Updated import path for SYS_HIDDEN_SEQ_NUM

Comments suppressed due to low confidence (1)

core/src/executor/datafusion/datafusion_impl/iceberg_physical_expr.rs:53

• The debug struct name doesn’t match the actual struct (IcebergTransformPhysicalExpr). Update to f.debug_struct("IcebergTransformPhysicalExpr") for consistency.

        f.debug_struct("IcebergPhysicalExpr")

[Copilot]

Calling .unwrap() on the transform result may cause a panic at runtime. Consider propagating errors (e.g., using ? and mapping to a DataFusion error) instead of unwrapping.

Suggested change

	.unwrap();
	.map_err(to_datafusion_error)?;