feat(tfl): export TflFeedItemType const

Replace hardcoded "tfl-alert" string with a
TflFeedItemType const object, matching the pattern
used by google-calendar and weatherkit packages.

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

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

@@ -1,12 +1,13 @@
 export { TflSource } from "./tfl-source.ts"
 export { TflApi } from "./tfl-api.ts"
 export type { TflLineId } from "./tfl-api.ts"
-export type {
-	ITflApi,
-	StationLocation,
-	TflAlertData,
-	TflAlertFeedItem,
-	TflAlertSeverity,
-	TflLineStatus,
-	TflSourceOptions,
+export {
+	TflFeedItemType,
+	type ITflApi,
+	type StationLocation,
+	type TflAlertData,
+	type TflAlertFeedItem,
+	type TflAlertSeverity,
+	type TflLineStatus,
+	type TflSourceOptions,
 } from "./types.ts"

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

@@ -15,6 +15,7 @@ import type {
 } from "./types.ts"
 
 import { TflApi, lineId } from "./tfl-api.ts"
+import { TflFeedItemType } from "./types.ts"
 
 const setLinesInput = lineId.array()
 
@@ -150,7 +151,7 @@ export class TflSource implements FeedSource<TflAlertFeedItem> {
 
 			return {
 				id: `tfl-alert-${status.lineId}-${status.severity}`,
-				type: "tfl-alert",
+				type: TflFeedItemType.Alert,
 				timestamp: context.time,
 				data,
 				signals,

packages/aris-source-tfl/src/types.ts

@@ -20,7 +20,13 @@ export interface TflAlertData extends Record<string, unknown> {
 	closestStationDistance: number | null
 }
 
-export type TflAlertFeedItem = FeedItem<"tfl-alert", TflAlertData>
+export const TflFeedItemType = {
+	Alert: "tfl-alert",
+} as const
+
+export type TflFeedItemType = (typeof TflFeedItemType)[keyof typeof TflFeedItemType]
+
+export type TflAlertFeedItem = FeedItem<typeof TflFeedItemType.Alert, TflAlertData>
 
 export interface TflSourceOptions {
 	apiKey?: string