perf: eliminate intermediate string allocations in hot paths
- Replace WriteString(fmt.Sprintf(...)) with fmt.Fprintf() across 7 files
to avoid intermediate string allocation (writes directly to Builder)
- Refactor telegram message composition from O(n²) += to strings.Builder
- Refactor device event formatting from += chain to strings.Builder
- Fix lint issues: misspell, whitespace, gofumpt, gci, unused func
## Benchmark Results
WriteString(Sprintf) vs Fprintf (10-iteration loop, 5 fields each):
old: 2480 ns/op 2823 B/op 16 allocs/op
new: 1841 ns/op 1860 B/op 6 allocs/op
→ 26% faster, 34% less memory, 63% fewer allocations
Telegram message build (+= vs strings.Builder):
AllMedia: old 403 ns/1104 B/10 allocs → new 118 ns/336 B/3 allocs (3.4x faster)
LongText: old 8309 ns/47232 B/10 allocs → new 1483 ns/8064 B/2 allocs (5.6x faster)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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