🐛 [Bug]: FiberHandler adaptor does not flush when using `SendStreamWriter`

[grivera64]

Bug Description

In the opposite direction of #3421, there is also a bug where adaptor.FiberHandler also does not support buffered streaming directly to a net/http handler.

How to Reproduce

Steps to reproduce the behavior:

1. Create a fiber handler that uses c.SendStreamWriter()
2. Use adaptor.FiberHandler() to convert to a http.Handler.
3. Call handler.ServerHTTP(w, r) within a net/http` handler func.
4. Run the binary and run curl localhost:3000/stream.

Expected Behavior

The expected behavior is to have the BodyStream run, if present. The data should come sent as a buffered stream as w is written to.

Fiber Version

v3.0.0-rc.2

Code Snippet (optional)

package main

import (
	"bufio"
	"fmt"
	"io"

	"time"

	"github.com/gofiber/fiber/v3"
	"github.com/gofiber/fiber/v3/middleware/adaptor"
	"net/http"
)

func main() {
	handler := adaptor.FiberHandler(func(c fiber.Ctx) error {
		c.Set("Content-Type", "text/plain; charset=utf-8")
		c.Set("Cache-Control", "no-cache")
		c.Set("Connection", "keep-alive")
		c.Set("Transfer-Encoding", "chunked")
		return c.SendStreamWriter(func(w *bufio.Writer) {
			for i := 1; i <= 10; i++ {
				msg := fmt.Sprintf("Line %d\n", i)
				_, err := w.WriteString(msg)
				if err != nil {
					if err == io.ErrClosedPipe {
						return
					}
					fmt.Println("net/http: write error:", err)
					return
				}
				err = w.Flush()
				if err != nil {
					if err == io.ErrClosedPipe {
						return
					}
					fmt.Println("net/http: flush error:", err)
					return
				}
				if i < 10 {
					time.Sleep(1 * time.Second)
				}
			}
		})
	})
	http.HandleFunc("/stream", func(w http.ResponseWriter, r *http.Request) {
		handler.ServeHTTP(w, r)
	})
	http.ListenAndServe(":3000", nil)
}

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my problem prior to opening this one.
• I understand that improperly formatted bug reports may be closed without explanation.