refactor: migrate aris-data-source-tfl to aris-source-tfl

Migrates TFL package from old DataSource interface to new FeedSource
interface for use with FeedEngine.

Changes:
- Rename package from @aris/data-source-tfl to @aris/source-tfl
- Replace TflDataSource class with TflSource implementing FeedSource
- Add dependency on @aris/source-location for LocationKey
- Use normalized priority values (0-1) instead of arbitrary numbers
- Update tests for FeedSource interface
- Update README.md with new package name

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

packages/aris-source-tfl/package.json

@@ -0,0 +1,16 @@
+{
+	"name": "@aris/source-tfl",
+	"version": "0.0.0",
+	"type": "module",
+	"main": "src/index.ts",
+	"types": "src/index.ts",
+	"scripts": {
+		"test": "bun test src/",
+		"fetch-fixtures": "bun run scripts/fetch-fixtures.ts"
+	},
+	"dependencies": {
+		"@aris/core": "workspace:*",
+		"@aris/source-location": "workspace:*",
+		"arktype": "^2.1.0"
+	}
+}