Add @aris/data-source-tfl package

TfL data source for tube, overground, and Elizabeth line alerts.

- Fetches line statuses and filters to minor/major delays and closures
- Sorts alerts by severity, then by proximity to user location
- Caches station data after first fetch
- Uses arktype for API response validation
- Supports API injection for testing

Co-authored-by: Ona <no-reply@ona.com>

packages/aris-data-source-tfl/src/index.ts

@@ -0,0 +1,11 @@
+export { TflDataSource } from "./data-source.ts"
+export { TflApi, type ITflApi, type TflLineStatus } from "./tfl-api.ts"
+export type {
+	TflAlertData,
+	TflAlertFeedItem,
+	TflAlertSeverity,
+	TflDataSourceConfig,
+	TflDataSourceOptions,
+	TflLineId,
+	StationLocation,
+} from "./types.ts"