fix apikit

[KARTIKrocks]

Fixed

• request — Race condition on globalConfig and globalPaginationConfig — added sync.RWMutex guards
• middleware — Logger responseWriter forwarded duplicate WriteHeader calls to underlying writer
• middleware — Retry-After header was hardcoded to "60" regardless of configured rate limit window
• middleware — itoa helper caused infinite recursion on math.MinInt — replaced with strconv.Itoa
• httpclient — Integer overflow in retry delay calculation when attempt count exceeded 62
• httpclient — Circuit breaker allowed multiple concurrent probes in half-open state (TOCTOU)
• response — File() Content-Disposition header injection on non-ASCII filenames — added RFC 5987 encoding
• server — Shutdown() returned immediately instead of waiting for graceful shutdown to complete
• request — IsValidEmail accepted display-name formats like "Alice" <a@b.com> — now requires bare address
• apitest — RequestBuilder.Build() used Header.Set in loop, dropping multi-value headers — changed to Header.Add