feat(sedona-raster-functions): add RS_ConvexHull and item-level CRS to RS_Envelope

[Kontinuation]

Summary

• RS_Envelope: Update to produce geometry output with item-level CRS propagated from the raster's CRS, instead of plain Wkb(Planar, None)
• RS_ConvexHull (new): Returns the convex hull polygon of a raster from its four corner world coordinates. Unlike RS_Envelope (axis-aligned bounding box), RS_ConvexHull preserves the actual raster footprint for skewed/rotated rasters. Also outputs with item-level CRS.

[Copilot]

Pull request overview

This PR enhances raster geometry functions by propagating CRS metadata and adds a new convex hull function. The changes ensure that geometry outputs preserve the coordinate reference system from input rasters rather than returning plain WKB geometries.

Changes:

• Modified RS_Envelope to propagate item-level CRS from rasters to output geometries
• Added RS_ConvexHull function that returns the actual raster footprint (preserving skew/rotation) instead of axis-aligned bounding box
• Both functions now return geometries with attached CRS metadata using the item_crs pattern

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
rust/sedona-raster-functions/src/rs_envelope.rs	Updated to propagate CRS metadata from raster to output WKB geometry
rust/sedona-raster-functions/src/rs_convexhull.rs	New function that computes convex hull polygon from raster corner coordinates with CRS propagation
rust/sedona-raster-functions/src/register.rs	Registered the new rs_convexhull function
rust/sedona-raster-functions/src/lib.rs	Added module declaration for rs_convexhull

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[paleolimbot]

Thank you!