Creating metronome marks in markup mode

New metronome marks can be created in markup mode, but they will not change the tempo in MIDI output.

\version "2.24"

\relative c' {
  \tempo \markup {
    \concat {
      (
      \smaller \general-align #Y #DOWN \note { 16. } #UP
      " = "
      \smaller \general-align #Y #DOWN \note { 8 } #UP
      )
    }
  }
  c1
  c4 c' c,2
}