[source-paypal-transaction] transactions stream exhausts retries on PayPal 429 rate limits due short default backoff

### Connector Name

source-paypal-transaction

### Connector Version

2.6.44

### What step the error happened?

During the sync

### Relevant information

The PayPal Transaction source is failing consistently while syncing the `transactions` stream.

The `balances` stream completes successfully, but `transactions` enters `RATE_LIMITED` and repeatedly fails with PayPal HTTP 429 responses. The retry behavior appears to be the default short exponential backoff sequence: 1s, 2s, 4s, 8s, 16s, then the connector gives up after 6 tries.

In one failed sync log there was 26 occurrences of each short backoff delay and 25 occurrences of:

`Giving up _send(...) after 6 tries`
`AirbyteTracedException: API rate limit exceeded.`

I believe the `transactions` stream is missing the same longer backoff strategy used elsewhere, for example:

```yaml
backoff_strategies:
- type: ConstantBackoffStrategy
backoff_time_in_seconds: 100
```

This is currently blocking transactions stream refresh.

### Relevant log output

```shell
2026-08-28 10:04:55 info Read 1 records from balances stream
2026-08-28 10:04:55 info Finished syncing balances
2026-08-28 10:04:55 info Syncing stream: transactions
2026-08-28 10:05:03 info Stream status TRACE with status RUNNING received of sub-type: RATE_LIMITED for stream transactions
2026-08-28 10:05:35 info Backing off _send(...) for 1.0s (airbyte_cdk.sources.streams.http.exceptions.RateLimitBackoffException: HTTP Status Code: 429. Error: Too many requests.)
2026-08-28 10:05:35 info Caught retryable error 'HTTP Status Code: 429. Error: Too many requests.' after 1 tries. Waiting 1 seconds then retrying...
2026-08-28 10:05:35 info Backing off _send(...) for 2.0s (airbyte_cdk.sources.streams.http.exceptions.RateLimitBackoffException: HTTP Status Code: 429. Error: Too many requests.)
2026-08-28 10:05:35 info Backing off _send(...) for 4.0s (airbyte_cdk.sources.streams.http.exceptions.RateLimitBackoffException: HTTP Status Code: 429. Error: Too many requests.)
2026-08-28 10:05:35 info Backing off _send(...) for 8.0s (airbyte_cdk.sources.streams.http.exceptions.RateLimitBackoffException: HTTP Status Code: 429. Error: Too many requests.)
2026-08-28 10:05:35 info Backing off _send(...) for 16.0s (airbyte_cdk.sources.streams.http.exceptions.RateLimitBackoffException: HTTP Status Code: 429. Error: Too many requests.)
2026-08-28 10:05:35 error Giving up _send(...) after 6 tries (airbyte_cdk.sources.streams.http.exceptions.RateLimitBackoffException: HTTP Status Code: 429. Error: Too many requests.)
2026-08-28 10:05:35 error Retries exhausted with backoff exception.
airbyte_cdk.utils.traced_exception.AirbyteTracedException: API rate limit exceeded.
```

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