refactor(rust/sedona-schema): centralize SedonaType CRS helpers

[Kontinuation]

This is a follow-up of #615 (comment).

Summary

• add SedonaType::crs() and SedonaType::is_item_crs() in sedona-schema so CRS extraction and item_crs detection live on the type itself
• replace duplicated matching logic in raster functions, expression handling, testing helpers, and the Python schema wrapper with the new SedonaType helpers
• add schema-level coverage for the new helper methods

Testing

• cargo test -p sedona-schema -p sedona-expr -p sedona-functions -p sedona-raster-functions -p sedona-testing
• cargo clippy -p sedona-schema -p sedona-expr -p sedona-functions -p sedona-raster-functions -p sedona-testing

[Copilot]

Pull request overview

This PR centralizes CRS extraction and item-level CRS wrapper detection on SedonaType in sedona-schema, then updates downstream crates (raster/functions/expr/testing + Python wrapper) to use those helpers to remove duplicated matching logic.

Changes:

• Added SedonaType::crs() and SedonaType::is_item_crs() plus schema-level tests for both helpers.
• Replaced repeated SedonaType matching logic across raster execution, expression parsing, and testing utilities with the new helpers.
• Simplified the Python schema wrapper CRS getter to rely on SedonaType::crs().

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
rust/sedona-schema/src/datatypes.rs	Adds crs() / is_item_crs() on SedonaType and tests covering the new helpers.
rust/sedona-schema/src/matchers.rs	Switches CRS extraction and item_crs detection to the new SedonaType helpers.
rust/sedona-raster-functions/src/executor.rs	Removes local CRS/item_crs helpers and uses SedonaType::crs() / is_item_crs() during argument handling.
rust/sedona-functions/src/executor.rs	Uses SedonaType::is_item_crs() to dispatch iteration logic for item-level CRS arrays.
rust/sedona-expr/src/item_crs.rs	Replaces struct-field-name matching with SedonaType::is_item_crs() in item_crs parsing helpers.
rust/sedona-testing/src/create.rs	Updates test value constructors to recognize item_crs via SedonaType::is_item_crs().
rust/sedona-testing/src/testers.rs	Updates geometry/geography scalar literal handling to use SedonaType::is_item_crs().
python/sedonadb/src/schema.rs	Uses SedonaType::crs() to implement the Python crs getter consistently.

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[paleolimbot]

Thank you!