⚡ Bolt: [performance improvement] Optimize SSE string building by replacing fmt.Sprintf

[rschumann]

💡 What: Replaced fmt.Sprintf with direct string concatenation and strconv.FormatInt/strconv.Itoa in SSE event building across all streaming translators.
🎯 Why: fmt.Sprintf is slower and allocates more memory due to reflection and parsing overhead. In hot paths like SSE event building for streaming APIs, this adds up quickly. String concatenation is faster and more memory-efficient.
📊 Impact: Reduces reflection overhead and per-chunk memory allocations, resulting in faster and more efficient streaming performance.
🔬 Measurement: This optimization can be verified using go test -bench comparing the memory allocations of fmt.Sprintf vs direct string concatenation.

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PR created automatically by Jules for task 17681111118757714226 started by @rschumann

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