Speed up compilation by replacing darling with attrs

[aatifsyed]

About a 25% saving:

$ hyperfine \
>    --warmup 1 \
>    --runs 10 \
>    --prepare 'git checkout attrs && cargo clean && rm Cargo.lock' \
>    --command-name attrs \
>    'cargo build --offline' \
>    --prepare 'git checkout master && cargo clean && rm Cargo.lock' \
>    --command-name master \
>    'cargo build --offline'
Benchmark 1: attrs
  Time (mean ± σ):      5.668 s ±  0.834 s    [User: 10.875 s, System: 2.352 s]
  Range (min … max):    4.863 s …  7.809 s    10 runs
 
Benchmark 2: master
  Time (mean ± σ):      7.090 s ±  0.174 s    [User: 12.745 s, System: 2.176 s]
  Range (min … max):    6.769 s …  7.323 s    10 runs
 
Summary
  attrs ran
    1.25 ± 0.19 times faster than master

Because we don't bottleneck compilation:

Note that I am the author of attrs

[jaemk]

hey @aatifsyed , you'll need to update the .github/workflows/build.yml like this https://github.com/jaemk/cached/pull/240/files#diff-5c3fa597431eda03ac3339ae6bf7f05e1a50d6fc7333679ec38e21b337cb6721L26-L38 to get the pipeline working again (unless that PR is merged before you see this)