Use interface for spatial index rather than concrete struct

[rm-hull]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @rm-hull, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the spatial indexing component by introducing an interface to abstract its functionality. This change improves the modularity and testability of the codebase, allowing for greater flexibility in choosing or implementing different spatial indexing algorithms without affecting the API consumers.

Highlights

• Architectural Refactoring: I've introduced a new SpatialIndex interface in spatial-index/codepoint.go. This interface defines the Search, SearchIter, and Len methods, abstracting the underlying spatial index implementation.
• Concrete Implementation Renaming: The previous concrete SpatialIndex struct has been renamed to RtreeSpatialIndex to clearly indicate its specific implementation using an R-tree. All methods previously associated with SpatialIndex are now associated with RtreeSpatialIndex.
• Interface Adoption in API: The cmd/api_server.go and routes/search.go files have been updated to use the new spatialindex.SpatialIndex interface type when creating and passing around the spatial index. This promotes loose coupling and makes it easier to swap out spatial index implementations in the future.

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[github-actions]

	Tests	Passed ✅	Skipped	Failed
JUnit Test Report	18 ran	18 passed	0 skipped	0 failed

Test	Result
JUnit Test Report
postcode-polygons/internal.TestDecompressFeatureCollection_Success	✅ passed
postcode-polygons/internal.TestDecompressFeatureCollection_FileNotFound	✅ passed
postcode-polygons/internal.TestDecompressFeatureCollection_InvalidBZ2	✅ passed
postcode-polygons/internal.TestCompressFeatureCollection_Success	✅ passed
postcode-polygons/internal.TestCompressFeatureCollection_ErrorOnCreate	✅ passed
postcode-polygons/internal.TestCompressFeatureCollection_And_DecompressFeatureCollection_RoundTrip	✅ passed
postcode-polygons/spatial-index.TestNewCodePointSpatialIndex_Success	✅ passed
postcode-polygons/spatial-index.TestNewCodePointSpatialIndex_BadZip	✅ passed
postcode-polygons/spatial-index.TestSearch	✅ passed
postcode-polygons/spatial-index.TestSearchIter_InvalidBounds	✅ passed
postcode-polygons/spatial-index.TestLen	✅ passed
postcode-polygons/spatial-index.Test_fromCodePointCSV	✅ passed
postcode-polygons/spatial-index.TestParseCSV_WithHeader_Success	✅ passed
postcode-polygons/spatial-index.TestParseCSV_WithoutHeader_Success	✅ passed
postcode-polygons/spatial-index.TestParseCSV_ParseError	✅ passed
postcode-polygons/spatial-index.TestParseCSV_MalformedLine	✅ passed
postcode-polygons/spatial-index.TestParseCSV_HeaderReadError	✅ passed
postcode-polygons/spatial-index.TestParseCSV_YieldStopsEarly	✅ passed

• View JUnit Test Report

[gemini-code-assist]

Code Review

This pull request introduces a SpatialIndex interface to decouple the spatial index implementation from its consumers, which is a great architectural improvement. The changes are consistently applied across the codebase. I have one suggestion to further improve the abstraction by modifying the constructor to return the interface type instead of the concrete implementation, which will fully hide the implementation details from consumers.

[coveralls]

Pull Request Test Coverage Report for Build 15948367623

Details

• 7 of 15 (46.67%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 32.112%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cmd/api_server.go	0	4	0.0%
routes/search.go	0	4	0.0%

Totals
Change from base Build 15945004373:	0.0%
Covered Lines:	149
Relevant Lines:	464

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💛 - Coveralls