Extract duplicate generateETag function from handler/static.go and
cache/file_cache.go into internal/utils/etag.go. Both functions were
identical, using strconv.AppendInt for zero-allocation ETag generation.
- Create utils.GenerateETag(modTime, size) as the unified implementation
- Update handler/static.go to call utils.GenerateETag
- Update cache/file_cache.go to call utils.GenerateETag
- Remove unused strconv import from static.go
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
