Connect API: /actions/run endpoint taking 6-10s for simple actions

## Description

When using the Pipedream Connect API to run actions, the POST `/connect/{project_id}/actions/run` endpoint takes **6-10 seconds** when `stash_id: ""` is included, but only **1.5 seconds** when `stash_id` is omitted.

## Root Cause Found

Sending `stash_id: ""` (empty string) to initialize a new stash causes a massive performance penalty.

| Request | Response Time |
|---------|---------------|
| Without `stash_id` | ~1.5s |
| With `stash_id: ""` | ~6-10s |
| With `stash_id: ""` | (not yet tested) |

## Environment

- API endpoint: `https://api.pipedream.com/v1/connect/{project_id}/actions/run`
- Action tested: `trengo-list-messages`

## Reproduction

**Fast request (~1.5s):**
```bash
curl -X POST 'https://api.pipedream.com/v1/connect/{project_id}/actions/run' \
-H 'Authorization: Bearer ...' \
-H 'Content-Type: application/json' \
-d '{
"id": "trengo-list-messages",
"configured_props": { ... },
"external_user_id": "..."
}'
```

**Slow request (~6-10s):**
```bash
curl -X POST 'https://api.pipedream.com/v1/connect/{project_id}/actions/run' \
-H 'Authorization: Bearer ...' \
-H 'Content-Type: application/json' \
-d '{
"id": "trengo-list-messages",
"configured_props": { ... },
"external_user_id": "...",
"stash_id": ""
}'
```

## Impact

We use `stash_id: ""` on the first action of a workflow to initialize a stash for sharing data between subsequent actions. This 5-8 second penalty on stash creation significantly impacts our workflow execution times.

## Expected Behavior

Creating a new stash (via `stash_id: ""`) should not add significant latency compared to requests without stash.

## Reference

The Pipedream Connect demo at https://pipedream.com/connect/demo?app=trengo&component=trengo-list-messages&tab=debug shows runtimes of 1-2 seconds, which matches our results when `stash_id` is omitted.