fix(cli): fix remote generation polling hang after task completion

[Swimburger]

Description

Fixes an infinite polling hang in fern generate where the CLI never detects task completion despite the Fiddle coordinator correctly returning "_type": "finished" status.

Root Cause

The fiddle-sdk's TaskStatus._visit() method calls visitor functions but does not await async handler results. When processUpdate() called await remoteTask.status._visit({...}), the await resolved immediately (the _visit return value is not the handler's Promise), so #isFinished was never set before the polling loop checked it — causing infinite polling.

Changes Made

• Replace _visit() with direct switch on status.type in RemoteTaskHandler.processUpdate() — this allows proper await of the async downloadFilesForTask call before setting #isFinished = true
• Add S3 download timeouts — timeout: 60_000 (connection) + AbortSignal.timeout(5 min) (overall) on both downloadZipForTask and downloadAndExtractZipToDirectory to prevent indefinite hangs on slow/stalled downloads
• Remove unused noop import, add assertNeverNoThrow for forward-compatible handling of unknown status types in the default case

-await remoteTask.status._visit<void | Promise<void>>({
-    notStarted: noop,
-    running: noop,
-    finished: async (finishedStatus) => {
-        // this async handler was never awaited by _visit()!
-        await downloadFilesForTask(...);
-        this.#isFinished = true; // set AFTER _visit() already returned
-    },
-    ...
-});
+const status = remoteTask.status;
+switch (status.type) {
+    case "finished": {
+        await downloadFilesForTask(...); // properly awaited now
+        this.#isFinished = true;         // set before returning
+        break;
+    }
+    ...
+}

Testing

• TypeScript compilation passes (pnpm turbo run compile --filter @fern-api/remote-workspace-runner)
• Biome lint passes
• Unit tests pass (pnpm turbo run test --filter @fern-api/remote-workspace-runner)

Link to Devin session: https://app.devin.ai/sessions/ac52847fd52a4366b0f8e9125af51345
Requested by: @Swimburger

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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.