Add ST_CRS

[jesspav]

Summary

Adding ST_CRS so that we can pull the full CRS object from geometry where SRIDs do not apply (for example with non-EPSG codes).

Issue: #29

Examples

> select ST_crs(ST_SetCrs(ST_GeomFromText('POINT (1 1)'), 'EPSG:4329')) as crs;
┌───────────┐
│    crs    │
│    utf8   │
╞═══════════╡
│ EPSG:4329 │
└───────────┘

> select ST_crs(ST_SetCrs(ST_GeomFromText('POINT (1 1)'), 'EPSG:4326')) as crs;
┌───────────┐
│    crs    │
│    utf8   │
╞═══════════╡
│ OGC:CRS84 │
└───────────┘


> select ST_crs(ST_SetSrid(ST_GeomFromText('POINT (1 1)'), null)) as crs;
┌──────┐
│  crs │
│ utf8 │
╞══════╡
│      │
└──────┘

[Copilot]

Pull Request Overview

This PR adds the ST_CRS function to return the coordinate reference system (CRS) of a geometry, which complements the existing ST_SRID function by supporting non-EPSG codes.

• Implements ST_CRS function that returns the full CRS object as a string
• Adds comprehensive test coverage for the new function
• Registers the new function in the default function set

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
rust/sedona-functions/src/st_srid.rs	Implements the core ST_CRS function logic and adds comprehensive unit tests
rust/sedona-functions/src/register.rs	Registers the new ST_CRS function in the default function set
python/sedonadb/tests/functions/test_transforms.py	Adds integration tests for both ST_SRID and ST_CRS functions

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[paleolimbot]

Great! Just a few minor comments!

[paleolimbot]

A few things to consider now or in a follow-up!

(Also the merge conflict so that CI can run!)

[paleolimbot]

Thank you!