Speed up brew tap for no arguments

[ZhongRuoyu]

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This provides a >3x speedup for brew tap with no arguments (i.e., when listing taps). It also makes the completion significantly faster.

$ hyperfine --warmup=3 --setup 'git checkout {branch}' --parameter-list branch master,brew-tap-speedup 'brew tap'
Benchmark 1: brew tap (branch = master)
  Time (mean ± σ):      1.405 s ±  0.080 s    [User: 0.561 s, System: 0.238 s]
  Range (min … max):    1.332 s …  1.549 s    10 runs

Benchmark 2: brew tap (branch = brew-tap-speedup)
  Time (mean ± σ):     404.1 ms ± 124.8 ms    [User: 107.9 ms, System: 200.7 ms]
  Range (min … max):   308.8 ms … 693.7 ms    10 runs

Summary
  brew tap (branch = brew-tap-speedup) ran
    3.48 ± 1.09 times faster than brew tap (branch = master)

[Rylan12]

This is great!

[MikeMcQuaid]

Great idea, thanks @ZhongRuoyu! A few more tweaks and then should be good to go.

[MikeMcQuaid]

Wonderful, thanks @ZhongRuoyu!