feat: support geospatial results on the kernel path

[cathleeny]

Summary

• add WithKernelGeospatialAsString and geospatialAsString for kernel-backed GEOMETRY / GEOGRAPHY results
• expose EWKT strings in string mode and raw WKB through database/sql in binary mode while preserving the canonical {srid,wkb} Arrow struct through GetArrowBatches
• preserve logical GEOMETRY / GEOGRAPHY column metadata and keep the option entirely client-side (it is never forwarded to SEA)
• pin local kernel builds to the exact kernel dependency commit below

Dependency

Depends on databricks/databricks-sql-kernel#361 at ad3bc6993bca95b810839feade77ccd0ab98ece5.

Keep this PR in draft until #361 is merged and a kernel bindings version containing that commit is available. The released per-platform Go kernel modules remain at 1.1.0 today; this PR intentionally does not invent a prerelease bindings version.

Validation

• golangci-lint: 0 issues
• go test ./...: passed
• kernel-tagged go test ./... against the exact [ES-1911239] Retry transient S3 errors on staging PUT/GET/REMOVE #361 rustls archive: passed
• live Reyden E2E against the exact [ES-1911239] Retry transient S3 errors on staging PUT/GET/REMOVE #361 archive: EWKT mode, binary WKB mode, logical type metadata, and nulls passed

[cathleeny]

Superseded by #492, which uses an upstream branch so repository CI credentials are available.