test: consolidate port allocation into shared test/testutil package (#8982)

* test: consolidate port allocation into shared test/testutil package

Move duplicated port allocation logic from 15+ test files into a single
shared package at test/testutil/. This fixes a port collision bug where
independently allocated ports could overlap via the gRPC offset
(port+10000), causing weed mini to reject the configuration.

The shared package provides:
- AllocatePorts: atomic allocation of N unique ports
- AllocateMiniPorts/MustFreeMiniPorts: gRPC-offset-aware allocation
  that prevents port A+10000 == port B collisions
- WaitForPort, WaitForService, FindBindIP, WriteIAMConfig, HasDocker

* test: address review feedback and fix FUSE build

- Revert fuse_integration change: it has its own go.mod and cannot
  import the shared testutil package
- AllocateMiniPorts: hold all listeners open until the entire batch is
  allocated, preventing race conditions where other processes steal ports
- HasDocker: add 5s context timeout to avoid hanging on stalled Docker
- WaitForService: only treat 2xx HTTP status codes as ready

* test: use global rand in AllocateMiniPorts for better seeding

Go 1.20+ auto-seeds the global rand generator. Using it avoids
identical sequences when multiple tests call at the same nanosecond.

* test: revert WaitForService status code check

S3 endpoints return non-2xx (e.g. 403) on bare GET requests, so
requiring 2xx caused the S3 integration test to time out. Any HTTP
response is sufficient proof that the service is running.

* test: fix gofmt formatting in s3tables test files

test/testutil/helpers.go

@@ -0,0 +1,105 @@
+package testutil
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"time"
+)
+
+const SeaweedMiniStartupTimeout = 45 * time.Second
+
+func HasDocker() bool {
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	cmd := exec.CommandContext(ctx, "docker", "version")
+	return cmd.Run() == nil
+}
+
+func FindBindIP() string {
+	addrs, err := net.InterfaceAddrs()
+	if err != nil {
+		return "127.0.0.1"
+	}
+	for _, addr := range addrs {
+		ipNet, ok := addr.(*net.IPNet)
+		if !ok || ipNet.IP == nil {
+			continue
+		}
+		ip := ipNet.IP.To4()
+		if ip == nil || ip.IsLoopback() || ip.IsLinkLocalUnicast() {
+			continue
+		}
+		return ip.String()
+	}
+	return "127.0.0.1"
+}
+
+func WriteIAMConfig(dir, accessKey, secretKey string) (string, error) {
+	iamConfigPath := filepath.Join(dir, "iam_config.json")
+	iamConfig := fmt.Sprintf(`{
+  "identities": [
+    {
+      "name": "admin",
+      "credentials": [
+        {
+          "accessKey": "%s",
+          "secretKey": "%s"
+        }
+      ],
+      "actions": [
+        "Admin",
+        "Read",
+        "List",
+        "Tagging",
+        "Write"
+      ]
+    }
+  ]
+}`, accessKey, secretKey)
+
+	if err := os.WriteFile(iamConfigPath, []byte(iamConfig), 0644); err != nil {
+		return "", err
+	}
+	return iamConfigPath, nil
+}
+
+func WaitForService(url string, timeout time.Duration) bool {
+	client := &http.Client{Timeout: 2 * time.Second}
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	ticker := time.NewTicker(500 * time.Millisecond)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return false
+		case <-ticker.C:
+			resp, err := client.Get(url)
+			if err == nil {
+				resp.Body.Close()
+				return true
+			}
+		}
+	}
+}
+
+func WaitForPort(port int, timeout time.Duration) bool {
+	deadline := time.Now().Add(timeout)
+	address := fmt.Sprintf("127.0.0.1:%d", port)
+	for time.Now().Before(deadline) {
+		conn, err := net.DialTimeout("tcp", address, 500*time.Millisecond)
+		if err == nil {
+			_ = conn.Close()
+			return true
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+	return false
+}