Refactor log parsing in devtool to use encoding/json

[osse101]

This PR replaces the fragile custom string manipulation logic for parsing JSON logs in cmd/devtool/analyze_logs.go with the standard encoding/json package. It unmarshals the JSON lines into a defined logEntry struct to extract values reliably, falling back to existing logic only for non-JSON lines. This significantly improves reliability, especially for JSON logs that might have commas or escaped quotes inside their field values. All project unit tests passed successfully.

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PR created automatically by Jules for task 9090923883623310275 started by @osse101

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