Handle batched mouse events

[wingdeans]

This snippet stops all events that are not 6 bytes long from being processed as mouse events.

However, some terminals may emit multiple mouse events per "tick."

• alacritty emits two events when a mouse down and mouse move occur simultaneously, dropping the event
• termux emits the mouse down and mouse up event simultaneously for mouse clicks (this stops all mouse clicks from registering)
  example of mouse click:

  (dlv) p string(buf)
  "\x1b[M +6\x1b[M#+6"
  

Reproducing

• build the "mouse" example with optimizations off -gcflags "all=-N -l"
• break on line 68 of mouse.go
• trigger breakpoint by moving mouse and pressing mouse button simultaneously

Expected Behaviour

Should register "batched" mouse events, like ncurses-based apps.