refactor(rust/sedona-raster-functions): extract CachedCrsToSRIDMapping and simplify SRID/CRS logic

[Kontinuation]

Summary

• Extract CachedCrsToSRIDMapping struct into sedona-schema::crs for reusable CRS-to-SRID caching, replacing ad-hoc HashMap caching in ST_SRID and duplicated logic in RS_SRID
• Refactor RS_SRID and RS_CRS in sedona-raster-functions to use early-return patterns instead of deeply nested match arms
• Add crs_str_ref() to RasterRefImpl for zero-copy CRS string access
• Make with_global_proj_engine generic (pub fn ... -> Result<R>) and public for external use
• Add test coverage for rasters with missing CRS and CRS without SRID

Dependencies

• Depends on refactor(rust/sedona-raster): Pre-downcast band metadata arrays in RasterStructArray #588 (pr2-better-band-metadata-ref)

[Copilot]

Pull request overview

Refactors CRS/SRID handling to reuse a shared CRS→SRID cache and simplify raster SRID/CRS UDF logic, while also exposing a public/global PROJ engine helper and adding tests for missing/unsupported CRS cases.

Changes:

• Added CachedCrsToSRIDMapping in sedona-schema::crs and updated SRID UDFs to use it.
• Simplified RS_SRID / RS_CRS raster UDF logic (early returns) and added raster CRS string ref accessor.
• Made with_global_proj_engine public + generic and added tests for missing CRS / CRS-without-SRID.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
rust/sedona-schema/src/crs.rs	Introduces reusable cached CRS→SRID mapping + tweaks CRS deserialization behavior.
rust/sedona-raster/src/array.rs	Refactors band metadata access and adds RasterRefImpl::crs_str_ref().
rust/sedona-raster-functions/src/rs_srid.rs	Updates RS_SRID/RS_CRS to use caching and early-return flow; adds tests.
rust/sedona-functions/src/st_srid.rs	Replaces per-batch HashMap caching with shared CachedCrsToSRIDMapping.
c/sedona-proj/src/st_transform.rs	Makes global PROJ engine helper public and returns generic Result<R>.
c/sedona-proj/src/lib.rs	Exposes st_transform module publicly.

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[paleolimbot]

Thank you!

[paleolimbot]

Can this be reverted? (I don't see a reference to with_global_proj_engine() in this PR?)

We should probably move the PROJ engine to its own public module and/or abstract it so we can switch to something faster for simple transforms.

[Kontinuation]

Good catch. We may need to make it pub later, but definitely not in this PR. I'll revert it.

[paleolimbot]

Is this used in this PR?

[Kontinuation]

No. I'll remove it.

[paleolimbot]

Not for this PR, but the abbreviated CRS should probably have this too (I have a batch-local cache for st_setsrid):

sedona-db/rust/sedona-functions/src/st_setsrid.rs

Lines 510 to 542 in cb713ef

	let mut known_abbreviated = HashMap::<String, String>::new();
	let string_value = crs_value.cast_to(&DataType::Utf8View, None)?;
	let string_array_ref = ColumnarValue::values_to_arrays(&[string_value])?;
	let string_view_array = as_string_view_array(&string_array_ref[0])?;
	let utf8_view_array = string_view_array
	.iter()
	.map(|maybe_crs| -> Result<Option<String>> {
	if let Some(crs_str) = maybe_crs {
	if crs_str == "0" {
	return Ok(None);
	}
	if let Some(abbreviated_crs) = known_abbreviated.get(crs_str) {
	Ok(Some(abbreviated_crs.clone()))
	} else if let Some(crs) = deserialize_crs(crs_str)? {
	let abbreviated_crs =
	if let Some(auth_code) = crs.to_authority_code()? {
	auth_code
	} else {
	crs_str.to_string()
	};
	known_abbreviated.insert(crs.to_string(), abbreviated_crs.clone());
	Ok(Some(abbreviated_crs))
	} else {
	Ok(None)
	}
	} else {
	Ok(None)
	}
	})
	.collect::<Result<StringViewArray>>()?;

[Kontinuation]

I'll handle it when implementing RS_SetSRID and RS_SetCRS.