feat: improve writing speed

[francisdb]

Improves the writing speed by keeping track of free sectors.
Adds write benchmark cargo bench

Related to #42

Further work is still needed to improve big stream writing. I think mostly the chaining code.

Before:

     Running benches/benchmark.rs (target/release/deps/benchmark-227a51791cd8dd8e)
Gnuplot not found, using plotters backend
Benchmarking write many smaller streams: Warming up for 3.0000 s
Warning: Unable to complete 100 samples in 5.0s. You may wish to increase target time to 7.3s, or reduce sample count to 60.
write many smaller streams
                        time:   [74.316 ms 74.338 ms 74.365 ms]
                        change: [+0.0742% +0.6368% +1.0568%] (p = 0.00 < 0.05)
                        Change within noise threshold.
Found 3 outliers among 100 measurements (3.00%)
  1 (1.00%) high mild
  2 (2.00%) high severe

write several medium streams
                        time:   [31.027 ms 31.121 ms 31.220 ms]
                        change: [−0.1073% +0.4565% +1.0339%] (p = 0.12 > 0.05)
                        No change in performance detected.
Found 3 outliers among 100 measurements (3.00%)
  2 (2.00%) high mild
  1 (1.00%) high severe

Benchmarking write large stream/size: Warming up for 3.0000 s
Warning: Unable to complete 10 samples in 5.0s. You may wish to increase target time to 21.8s.
write large stream/size time:   [2.2079 s 2.2408 s 2.2698 s]
                        thrpt:  [112.78 MiB/s 114.24 MiB/s 115.94 MiB/s]
                 change:
                        time:   [−2.1473% −0.2973% +1.3868%] (p = 0.75 > 0.05)
                        thrpt:  [−1.3678% +0.2982% +2.1944%]
                        No change in performance detected.

After:

     Running benches/benchmark.rs (target/release/deps/benchmark-227a51791cd8dd8e)
Gnuplot not found, using plotters backend
Benchmarking write many smaller streams: Warming up for 3.0000 s
Warning: Unable to complete 100 samples in 5.0s. You may wish to increase target time to 7.3s, or reduce sample count to 60.
write many smaller streams
                        time:   [72.948 ms 72.974 ms 73.008 ms]
                        change: [−1.8865% −1.8352% −1.7804%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
  1 (1.00%) high mild
  2 (2.00%) high severe

write several medium streams
                        time:   [12.985 ms 13.070 ms 13.163 ms]
                        change: [−58.315% −58.003% −57.691%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 9 outliers among 100 measurements (9.00%)
  8 (8.00%) high mild
  1 (1.00%) high severe

Benchmarking write large stream/size: Warming up for 3.0000 s
Warning: Unable to complete 10 samples in 5.0s. You may wish to increase target time to 18.5s.
write large stream/size time:   [1.8420 s 1.8530 s 1.8629 s]
                        thrpt:  [137.42 MiB/s 138.15 MiB/s 138.98 MiB/s]
                 change:
                        time:   [−18.456% −17.307% −15.995%] (p = 0.00 < 0.05)
                        thrpt:  [+19.040% +20.930% +22.633%]
                        Performance has improved.

[mdsteele]

Thanks!

[francisdb]

I plan to work on a follow-up PR that improves big file writing.