[-] fix file leak in GetPathUnderlyingDeviceID, fixes #1185 (#1192)

* add file close to avoid leak

* add tests for psutil_linux

* add 'os' import to psutil_test.go

* skip tests on non-Linux OS

---------

Co-authored-by: Pavlo Golub <pavlo.golub@gmail.com>

Author: Mazen050

internal/reaper/psutil_linux.go

@@ -10,6 +10,8 @@ func GetPathUnderlyingDeviceID(path string) (uint64, error) {
 	if err != nil {
 		return 0, err
 	}
+	defer fp.Close()
+
 	fi, err := fp.Stat()
 	if err != nil {
 		return 0, err

internal/reaper/psutil_test.go

@@ -1,12 +1,14 @@
 package reaper
 
 import (
+	"runtime"
 	"slices"
 	"testing"
 
 	"github.com/cybertec-postgresql/pgwatch/v5/internal/metrics"
 
 	"maps"
+	"os"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -73,3 +75,34 @@ func TestGetLoadAvgLocal(t *testing.T) {
 	resultKeys := slices.Collect(maps.Keys(result[0]))
 	a.ElementsMatch(resultKeys, expectedKeys)
 }
+
+func TestGetPathUnderlyingDeviceID(t *testing.T) {
+	if runtime.GOOS != "linux" {
+		t.Skip("GetPathUnderlyingDeviceID is not implemented")
+	}
+	a := assert.New(t)
+	tmpDir := t.TempDir()
+	createFile := func(name string) string {
+		f, err := os.CreateTemp(tmpDir, name)
+		a.NoError(err)
+		defer f.Close()
+		return f.Name()
+	}
+
+	file1Path := createFile("file1")
+	devID1, err := GetPathUnderlyingDeviceID(file1Path)
+	a.NoError(err)
+
+	file2Path := createFile("file2")
+	devID2, err := GetPathUnderlyingDeviceID(file2Path)
+	a.NoError(err)
+	a.Equal(devID1, devID2)
+}
+
+func TestGetPathUnderlyingDeviceID_NotFound(t *testing.T) {
+	if runtime.GOOS != "linux" {
+		t.Skip("GetPathUnderlyingDeviceID is not implemented")
+	}
+	_, err := GetPathUnderlyingDeviceID("/this/path/should/not/exist/nofile")
+	assert.Error(t, err)
+}