Function parse

parse(content: string): { qos: number }
Parser for qos tags - defines MQTT Quality of Service level

This parser handles the qos tag that defines MQTT QoS levels. It extracts:
- QoS level (0, 1, or 2)
- Validates QoS value is within allowed range
Parameters
- content: string
  Raw content from the qos tag
Returns { qos: number }
Parsed QoS information or null if parsing fails
Example: QoS 0 - At most once delivery
```
// Input: "0"
// Output: { qos: 0 }
```
Example: QoS 1 - At least once delivery
```
// Input: "1"
// Output: { qos: 1 }
```
Example: QoS 2 - Exactly once delivery
```
// Input: "2"
// Output: { qos: 2 }
```
Since
4.1.0

Public
- Defined in core/parsers/mqtt_qos.ts:33