[codex] Add bounds selection support

[0xSwego]

Summary

Adds first-class rectangular lon/lat bounds support to GeoSelectionOptions so callers can use client.selectDataset({ selection: { bounds: [west, south, east, north] } }) instead of manually loading and calling GeoTemporalDataset.rectangle().

Changes

• Adds tuple and object forms for bounds plus optional coordinate key overrides.
• Applies bounds inside GeoTemporalDataset.select() through the existing rectangle selection implementation.
• Rejects ambiguous selections that specify both point and bounds.
• Updates the fake dataset helper to support array coordinate selections used by rectangle tests.
• Documents the selectDataset bounds usage.

Validation

• npx vitest run tests/selection-options.test.ts
• npm run build