Fix final-measure spacing in docs

[trevorbaca]

• [ ] spacing of final measures in doc examples is too tight because baca.spacing() thinks there is a phantom measure when there is not; the 1/4 spacing in the last measure here should be 1/12 instead:

  \context Score = "Score"
  {
  \context Staff = "Music_Staff"
  <<
      \context Voice = "Global_Skips"
      {
          \baca-new-spacing-section #1 #12
          \time 4/8
          s1 * 1/2
          \baca-new-spacing-section #1 #12
          \time 3/8
          s1 * 3/8
          \baca-new-spacing-section #1 #12
          \time 4/8
          s1 * 1/2
          \baca-new-spacing-section #1 #4
          \time 3/8
          s1 * 3/8
      }
      \context Voice = "Music_Voice"
      {
          {
              c'2
              - \tweak color #(x11-color 'blue)
              \p
              - \tweak to-barline ##t
              - \tweak stencil #constante-hairpin
              \<
              r4.
              \!
              d'2
              - \tweak color #(x11-color 'blue)
              \f
              - \tweak to-barline ##t
              - \tweak stencil #constante-hairpin
              \<
              r4.
              \!
          }
      }
  >>
  }

  The generating code looks like this:

  
  score = baca.docs.make_empty_score(1)
  commands = baca.CommandAccumulator(
  time_signatures=[(4, 8), (3, 8), (4, 8), (3, 8)],
  )

commands( "Music_Voice", baca.hairpin( "p -- niente", abjad.tweak(True).to_barline, selector=baca.selectors.leaves((None, 2)), ), baca.hairpin( "f -- niente", abjad.tweak(True).to_barline, selector=baca.selectors.leaves((2, None)), ), baca.pitches("C4 D4"), baca.skeleton("{ c2 r4. c2 r4. }"), )

, = baca.interpreter( score, commands.commands, commands.time_signatures, move_global_context=True, remove_tags=baca.tags.documentation_removal_tags(), spacing=baca.SpacingSpecifier(fallback_duration=(1, 12)), )