message: verilog_project: Mark InMemoryVerilogSourceFile class final
  InMemoryVerilogSourceFile class is implemented for testing purposes.
  Marking it final as we don't expect to derive it further.
diff: @@ -149,7 +149,7 @@ std::ostream& operator<<(std::ostream&, const VerilogSourceFile&);
  // An in-memory source file that doesn't require file-system access,
  // nor create temporary files.
  -class InMemoryVerilogSourceFile : public VerilogSourceFile {
  +class InMemoryVerilogSourceFile final : public VerilogSourceFile {
  public:
  // filename can be fake, it is not used to open any file.
  InMemoryVerilogSourceFile(absl::string_view filename,
  