smb: optimize smb mount performance by avoiding stat checks during initialization

add IsPathDir function and tests for trailing slash optimization

backend/smb/smb_internal_test.go

@@ -0,0 +1,41 @@
+// Unit tests for internal SMB functions
+package smb
+
+import "testing"
+
+// TestIsPathDir tests the isPathDir function logic
+func TestIsPathDir(t *testing.T) {
+	tests := []struct {
+		path     string
+		expected bool
+	}{
+		// Empty path should be considered a directory
+		{"", true},
+
+		// Paths with trailing slash should be directories
+		{"/", true},
+		{"share/", true},
+		{"share/dir/", true},
+		{"share/dir/subdir/", true},
+
+		// Paths without trailing slash should not be directories
+		{"share", false},
+		{"share/dir", false},
+		{"share/dir/file", false},
+		{"share/dir/subdir/file", false},
+
+		// Edge cases
+		{"share//", true},
+		{"share///", true},
+		{"share/dir//", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.path, func(t *testing.T) {
+			result := isPathDir(tt.path)
+			if result != tt.expected {
+				t.Errorf("isPathDir(%q) = %v, want %v", tt.path, result, tt.expected)
+			}
+		})
+	}
+}