This improves the load time of most brew commands. For an example of
one of the simplest commands this speeds up:
Without Bootsnap:
```
$ hyperfine 'git checkout master; brew help' 'git checkout optimise_requires; brew help'
Benchmark 1: git checkout master; brew help
Time (mean ± σ): 525.0 ms ± 35.8 ms [User: 229.9 ms, System: 113.1 ms]
Range (min … max): 465.3 ms … 576.6 ms 10 runs
Benchmark 2: git checkout optimise_requires; brew help
Time (mean ± σ): 383.3 ms ± 25.1 ms [User: 133.0 ms, System: 72.1 ms]
Range (min … max): 353.0 ms … 443.6 ms 10 runs
Summary
git checkout optimise_requires; brew help ran
1.37 ± 0.13 times faster than git checkout master; brew help
```
With Bootsnap:
```
$ hyperfine 'git checkout master; brew help' 'git checkout optimise_requires; brew help'
Benchmark 1: git checkout master; brew help
Time (mean ± σ): 386.0 ms ± 30.9 ms [User: 130.2 ms, System: 93.8 ms]
Range (min … max): 359.5 ms … 469.3 ms 10 runs
Benchmark 2: git checkout optimise_requires; brew help
Time (mean ± σ): 330.2 ms ± 32.4 ms [User: 93.4 ms, System: 73.0 ms]
Range (min … max): 302.9 ms … 413.9 ms 10 runs
Summary
git checkout optimise_requires; brew help ran
1.17 ± 0.15 times faster than git checkout master; brew help
```
- Rename use of "preinstall" to "auto update". The original "preinstall"
naming came from the fact that we used to only auto-update before
`brew install` but now that it's many commands: this is more confusing
than useful.
- Add `HOMEBREW_NO_UPDATE_REPORT_ONLY_INSTALLED` and remove
`HOMEBREW_UPDATE_REPORT_ONLY_INSTALLED`; the latter is now the default
and the prior provides an opt-out for better output, performance and
avoiding reading potentially untrusted formulae.
- Add `HOMEBREW_UPDATE_FORMULA_VERSION_CHECKS` and don't check formula
versions by default for better performance by default.
Co-authored-by: Eric Knibbe <3324775+EricFromCanada@users.noreply.github.com>
Co-authored-by: Sam Ford <1584702+samford@users.noreply.github.com>
