🐛 Normal HTTP/2 stream cancellations (error code 0 / NO_ERROR) are logged at ERR level

### Describe the bug
When a remote client gracefully terminates a long-lived HTTP/2 stream (such as closing a browser tab tailing Server-Sent Events, WebSockets, or live log streams), cloudflared logs the stream cancellation at ERR severity. Per RFC 9113 (HTTP/2), error code 0x0 (NO_ERROR) indicates that the stream closure is non-erroneous and intentional. Logging these events as system errors creates false positives in monitoring systems (e.g., Datadog, Grafana) and unnecessarily pollutes log outputs.

### To Reproduce
Steps to reproduce the behavior:

- Proxy an application with long-lived HTTP/2 streaming or log-tailing endpoints via cloudflared (e.g., Home Assistant's /api/hassio/addons/.../logs/follow).
- Open the streaming endpoint in a web browser.
- Close the browser tab or refresh the page to trigger a client-side stream reset (RST_STREAM).

See error in cloudflared stdout/stderr.

### Expected behavior
RST_STREAM frames with error code 0 (NO_ERROR) should be recognized as normal client disconnects and logged under DEBUG or INFO severity rather than ERR.

### Environment and versions

OS: Linux (Home Assistant OS)
Architecture: ARM64 / x86_64
Version: 2026.8.2

### Logs and errors
```
2026-08-25T08:07:02Z ERR error="stream 41 canceled by remote with error code 0" connIndex=3 event=1 ingressRule=0 originService=http://homeassistant
2026-08-25T08:07:02Z ERR Request failed error="stream 41 canceled by remote with error code 0" connIndex=3 dest=https://ha.example.com/api/hassio/addons/cloudflared/logs/follow?lines=100 event=0 ip=198.41.192.77 type=http
```

### Additional context
This occurs because the ingress proxy layer routes any non-nil stream error return code directly to the error logger without filtering for HTTP/2 0x0 (NO_ERROR) status codes.

Start by tracing the ingress proxy layer's handling of non-nil stream errors during the provided long-lived HTTP/2 streaming reproduction. Verify behavior with a client that closes a browser tab or refreshes an SSE, WebSocket, or log stream; done means RST_STREAM error code 0 is logged at DEBUG or INFO instead of ERR, while other failures remain errors.

Written by the indexing model from the issue text.