feat(crawler): add canceled context to Visit func

[DmitriyLewen]

Description

When we get error from Visit function we close c.urlCh.
But there are cases when another Visit function tries to write to c.urlCh before we return error.
In this case we get panic instead of error.
e.g. - https://github.com/aquasecurity/trivy-java-db/actions/runs/8041756834/job/21961450007#step:5:619

To avoid this case - we need to add context with cancel function for Visit function.

[knqyf263]

Suggested change

	ctx, ctxCancelFunc := context.WithCancel(ctx)
	ctx, cancel := context.WithCancel(ctx)

nit: I think cancel is used conventionally.
https://go.dev/doc/database/cancel-operations

[DmitriyLewen]

Done - 8f9c98b

[knqyf263]

What if just checking context here?

Suggested change

	go func() {
	for _, child := range children {
	c.urlCh <- url + child
	}
	}()
	go func() {
	for _, child := range children {
	select {
	// Context can be canceled if we receive an error from another Visit function.
	case <-ctx.Done():
	return
	default:
	c.urlCh <- url + child
	}
	}
	}()

[DmitriyLewen]

I thought about this too.
I was worried that we need to stop func immediately after receiving the cancel function.
But after making HTTP requests context-sensitive (262f22d), we can move it into this loop.

Did this in c4a4202.

[knqyf263]

It is a good opportunity to make the HTTP request context-aware.

Suggested change

	resp, err := c.http.Get(url)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
	return xerrors.Errorf("unable to new HTTp request: %w", err)
	}
	if err = client.Do(req); err != nil {

[DmitriyLewen]

Good point!
Created this in 262f22d.