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/scripts/fetch-fixtures.ts

@@ -0,0 +1,35 @@
+// Fetches real TfL API responses and saves them as test fixtures
+
+const TEST_LINES = ["northern", "central", "elizabeth"]
+const BASE_URL = "https://api.tfl.gov.uk"
+
+async function fetchFixtures() {
+	console.log("Fetching line statuses...")
+	const statusRes = await fetch(`${BASE_URL}/Line/${TEST_LINES.join(",")}/Status`)
+	const lineStatuses = await statusRes.json()
+
+	console.log("Fetching stop points...")
+	const stopPoints: Record<string, unknown> = {}
+	for (const lineId of TEST_LINES) {
+		console.log(`  Fetching ${lineId}...`)
+		const res = await fetch(`${BASE_URL}/Line/${lineId}/StopPoints`)
+		stopPoints[lineId] = await res.json()
+	}
+
+	const fixtures = {
+		fetchedAt: new Date().toISOString(),
+		lineStatuses,
+		stopPoints,
+	}
+
+	const path = new URL("../fixtures/tfl-responses.json", import.meta.url)
+	await Bun.write(path, JSON.stringify(fixtures, null, "\t"))
+
+	console.log(`\nFixtures saved to fixtures/tfl-responses.json`)
+	console.log(`  Line statuses: ${(lineStatuses as unknown[]).length} lines`)
+	for (const [lineId, stops] of Object.entries(stopPoints)) {
+		console.log(`  ${lineId} stops: ${(stops as unknown[]).length}`)
+	}
+}
+
+fetchFixtures().catch(console.error)