Phase 6: MapPhase - Refactor to Polars

[mattsan-dev]

Overview
The FilterPhase step now produces data using Polars LazyFrames, but the MapPhase step still uses the legacy implementation and cannot process this new output. To keep the pipeline consistent and efficient, the MapPhase phase must be updated to use the Polars version. This will keep existing behaviour while modernising the underlying process.

Tech Approach

• Update digital_land/phase/MapPhase.py so it delegates to the Polars parse implementation.
• Implement the full MapPhase logic inside digital_land/phase_polars/transform/MapPhase.py.
• Convert existing MapPhase rules into Polars lazy transformations.
• Ensure the MapPhase phase accepts the LazyFrame produced by the new normalise step.
• Keep the same public interface so no downstream code needs changing.

Acceptance Criteria/Tests

• MapPhase phase accepts the normalise phase LazyFrame without errors.
• Legacy MapPhase behaviour is reproduced using Polars.
• Outputs match the legacy MapPhase phase (apart from expected improvements).
• No Pandas or row‑based Python operations are used.
• Add test cases
• Refactored code complies with project formatting and style standards (black/flake8/pep)

Resourcing & Dependencies
Depends on ConcatField phase, no external teams.

[lakshmi-kovvuri1]

Refactored digital_land/phase_polars/transform/map.py to use new Polars Lazy df method. The Polars refactor includes Column normalisation, Explicit column mapping, Implicit field matching, Coordinate pair handling and Audit logging, preserving existing business logic.after map phase, the polars lazy frame has column from prefix to 'site-prefix'

[lakshmi-kovvuri1]

@VENKAT-AVVARI-190825
We have added a unit and integration test case for this one (tests/unit/phase_polars/transform/map.py) please confirm that this is working and make any changes necessary.
tests/integration/phase_polars/transform/test_map.py
tests/unit/phase_polars/transform/test_map.py
Please also check that the refactored code complies with project formatting and style standards (black/flake8/pep) and make any necessary changes.