perf: open popup window and run hooks in a single execution

[loichyan]

Generally, adding tmux calls will also increase the latency when opening a popup window, as shown below:

Before this PR:

$ hyperfine --shell=/bin/sh --warmup=3 "./src/toggle.sh -E --before-open='run true' --on-init='detach' --after-close='run true'"
Benchmark 1: ./src/toggle.sh -E --before-open='run true' --on-init='detach' --after-close='run true'
  Time (mean ± σ):      64.1 ms ±  17.8 ms    [User: 17.1 ms, System: 24.2 ms]
  Range (min … max):    38.5 ms …  94.8 ms    70 runs

After:

$ hyperfine --shell=/bin/sh --warmup=3 "./src/toggle.sh -E --before-open='run true' --on-init='detach' --after-close='run true'"
Benchmark 1: ./src/toggle.sh -E --before-open='run true' --on-init='detach' --after-close='run true'
  Time (mean ± σ):      39.7 ms ±   2.9 ms    [User: 11.7 ms, System: 12.0 ms]
  Range (min … max):    33.1 ms …  45.4 ms    82 runs

A potential downside of this PR is that the commands specified in a hook must not affect the subsequent tmux commands. Since the two hooks subject to this limitation are rarely used, and few tmux commands have such an influence, it is acceptable to proceed.