support metric queries and numeric values

[kmlx]

I've started playing with this server and received an error when running the following query in loki_query:

{
  "query": "sum by (container) (count_over_time({cluster=\"mia2\"} | detected_level=\"error\" [5m]))",
  "start": "-5m"
}

query execution failed: json: cannot unmarshal number into Go struct field LokiEntry.data.result.values of type string

This error suggests that the server can't properly serialize numeric results from aggregations. Which I have confirmed by outputting raw loki results.

Hopefully this PR solves or at least starts the discussion towards solving this issue.

In this PR we will find the following:

• Support both Stream and Metric label fields in LokiEntry
• Handle numeric values in addition to log strings in Values array
• Detect timestamp format (seconds vs nanoseconds) for proper parsing
• Update formatLokiResults to work with both log and metric query results
• Add comprehensive tests for numeric values and metric query handling

Please have a look and let me know if any changes are needed or a different direction is preferred.

[CLAassistant]

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