Increase optimization level

[gosuwachu]

I know this is super low hanging fruit so I am probably missing something, but why was it set to 0?

[gosuwachu]

16e00de Speedup build times by not optimizing build dependencies

I think this project is now at a point where you probably want to increase runtime performance :)

[Byron]

Yes, indeed, it's about time! Great catch :D.

In practice, the difference on big(ish) directories is not measurable, and with small repositories it's a little faster but those 0.5ms aren't going to relevant to any human.

❯ hyperfine -w1 target/release/dua dua  -N
Benchmark 1: target/release/dua
  Time (mean ± σ):       7.6 ms ±   0.4 ms    [User: 7.0 ms, System: 26.0 ms]
  Range (min … max):     6.8 ms …   9.6 ms    312 runs

Benchmark 2: dua
  Time (mean ± σ):       8.2 ms ±   0.4 ms    [User: 7.1 ms, System: 26.1 ms]
  Range (min … max):     7.5 ms …   9.1 ms    352 runs

Summary
  target/release/dua ran
    1.08 ± 0.08 times faster than dua

dua-cli ( increase-optimzation-level) [$] took 5s
❯ hyperfine -w1 'target/release/dua ~/dev/github.com/WebKit' 'dua ~/dev/github.com/WebKit'
Benchmark 1: target/release/dua ~/dev/github.com/WebKit
  Time (mean ± σ):      2.359 s ±  0.031 s    [User: 0.668 s, System: 16.249 s]
  Range (min … max):    2.328 s …  2.422 s    10 runs

Benchmark 2: dua ~/dev/github.com/WebKit
  Time (mean ± σ):      2.347 s ±  0.006 s    [User: 0.668 s, System: 16.460 s]
  Range (min … max):    2.339 s …  2.361 s    10 runs

Summary
  dua ~/dev/github.com/WebKit ran
    1.00 ± 0.01 times faster than target/release/dua ~/dev/github.com/WebKit

The compile times change from 22s (-O0) to 24s (-O3), which I think is negligible.

On the basis on the slightly improved startup times I think this should be merged.