message: Clear cached runs after translate_y
  "While re-reading the code, I found out that I forgot to do clear cached runs
  after translate_y in c360b7588ff8d389b49a4ed60cdee51401a5e172."
diff: @@ -440,6 +440,8 @@ namespace til // Terminal Implementation Library. Also: "Today I Learned"
  _bits.set(_bits.size() - newBits, newBits, true);
  }
  }
  +
  + _runs.reset(); // reset cached runs on any non-const method
  }
  til::size _sz;
  