refactor: replace magic numbers with named constants in bodyAllowedForStatus

Use http.StatusContinue and http.StatusOK instead of hardcoded 100 and
199 for the 1xx informational status range check, consistent with the
pattern already used in logger.go.

Fixes #4489

context.go

@@ -1058,7 +1058,7 @@ func (c *Context) requestHeader(key string) string {
 // bodyAllowedForStatus is a copy of http.bodyAllowedForStatus non-exported function.
 func bodyAllowedForStatus(status int) bool {
 	switch {
-	case status >= 100 && status <= 199:
+	case status >= http.StatusContinue && status < http.StatusOK:
 		return false
 	case status == http.StatusNoContent:
 		return false