refactor!: move import progress from HTTP API to JS API

This is the next step in [a larger refactor][0] where we replace the
HTTP API with a JS one.

[0]: #111

BREAKING CHANGE: `GET /imports/progress/:importId` replaced with
  `getImportProgress()`

API.md

@@ -162,50 +162,3 @@ As of now, only [MBTiles](https://github.com/mapbox/mbtiles-spec) files are supp
   - `y: number`: The y coordinate of the tile.
 
 Retrieve a tile for a given tileset. Note that this is usually used by a map client (based on a style definition) and not directly by the end user ([more info](https://docs.mapbox.com/mapbox-gl-js/style-spec/sources/)).
-
----
-
-## Imports
-
-### `GET /imports/progress/:importId`
-
-- Params:
-  - `importId: string`: The ID for the desired import.
-
-Subscribe to progress information for an import. This is a [Server-Sent Events (SSE)](https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events) endpoint, so it's expected to be used with an [EventSource](https://developer.mozilla.org/en-US/docs/Web/API/EventSource) by the client.
-
-Messages that are received will have a `data` field with the following structure when deserialized:
-
-- `type: string`: Type indicating the type of progress message. Can be one of the following values:
-  - `"progress"`: Import is still in progress
-  - `"complete"`: Import is complete
-  - `"error"`: Error occurred during import
-- `importId: string`: ID for import
-- `soFar: number`: Number of assets successfully imported so far
-- `total: number`: Total number of assets to be imported
-
-If a requested import is already completed or has errored, responds with `204 No Content`, which should prevent the event source from attempting to reconnect. Generally, the client should explicitly close the event source when:
-
-1. Receiving a message and the deserialized `type` value in the event data is either `"complete"` or `"error"`.
-2. Receiving an error
-
-```js
-const evtSource = new EventSource(
-  'http://localhost:3000/imports/progress/some-import-id'
-)
-
-evtSource.onmessage = (event) => {
-  const message = JSON.parse(event.data)
-
-  if (message.type === 'complete' || message.type === 'error') {
-    evtSource.close()
-    return
-  }
-
-  // Do something with message...
-}
-
-evtSource.onerror = (event) => {
-  evtSource.close()
-}
-```

package.json

@@ -50,6 +50,7 @@
     "fastify-plugin": "^3.0.1",
     "got": "^11.8.5",
     "is-url": "^1.2.4",
+    "iterpal": "^0.3.0",
     "make-promises-safe": "^5.1.0",
     "mem": "^8.1.1",
     "piscina": "^3.2.0",
@@ -91,7 +92,7 @@
     "prisma-erd-generator": "^1.2.3",
     "standard-version": "^9.5.0",
     "tap-arc": "^0.3.5",
-    "tape": "^5.7.5",
+    "tape": "^5.7.4",
     "tmp": "^0.2.1",
     "ts-node": "^9.1.1",
     "ts-node-dev": "^1.1.8",