feat: support geospatial results on the kernel path

[cathleeny]

Summary

• add the kernel-only geospatial_as_string connection option
• expose EWKT strings in string mode and canonical {"srid": int, "wkb": bytes} values in binary mode
• preserve logical GEOMETRY / GEOGRAPHY Arrow metadata and keep the option entirely client-side (it is never forwarded to SEA)
• fail clearly when an explicit representation is requested with an older kernel wheel

Dependency

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

Keep this PR in draft until #361 is merged and a Python kernel wheel containing that commit is available. The released kernel wheel remains at 1.1.0 today; this PR intentionally does not invent a prerelease wheel version.

Validation

• mypy: 67 source files passed
• unit suite: 1,023 passed, 4 skipped, 1 deselected
• Black on changed Python files: passed
• real-kernel routing test against the exact version 2.9.4 #361 extension: passed
• live Reyden E2E against the exact version 2.9.4 #361 extension: EWKT and binary struct modes passed through both direct Arrow-scalar and pandas row conversion paths, including Arrow metadata and nulls