perf(tarball): use tokio::task::spawn_blocking

[KSXGitHub]

Thanks @TmLev for the suggestion.

The benchmark proved that spawn_blocking does improve the performance, even if it's only slightly.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (bd7002a) 87.01% compared to head (aca2c2b) 87.01%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #203      +/-   ##
==========================================
- Coverage   87.01%   87.01%   -0.01%     
==========================================
  Files          56       56              
  Lines        2827     2826       -1     
==========================================
- Hits         2460     2459       -1     
  Misses        367      367              

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[github-actions]

Micro-Benchmark Results

Linux

group                          main                                   pr
-----                          ----                                   --
tarball/download_dependency    1.01      6.8±0.43ms   641.9 KB/sec    1.00      6.7±0.19ms   648.4 KB/sec

[github-actions]

Integrated-Benchmark Report (Linux)

Scenario: Frozen Lockfile

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
pacquet@HEAD	146.9 ± 8.6	132.7	163.9	1.10 ± 0.09
pacquet@main	133.3 ± 8.1	121.4	145.7	1.00

BENCHMARK_REPORT.json

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[TmLev]

Here are a few general rules of thumb I follow for I/O operations:

1. Tokio tasks excel at Network I/O. If you need to fetch something or update a registry/index, use them.
2. Async File I/O is another story – the issue often stems from the API provided by the OS. For extensive file operations, it may be better to use tokio::spawn_blocking with a synchronous version. However, tasks should never directly use std::fs as it blocks the worker thread. For minor file operations, tokio::fs is the preferred choice.
   Details

   
3. For significant CPU-bound computations, it's advisable to offload them to a specialized thread pool, like Rayon. Here's an example of mixing Tokio with Rayon: https://ryhl.io/blog/async-what-is-blocking/#the-rayon-crate.
4. Cloning numerous Strings incurs a real performance hit. If Strings need to be shared between threads/tasks but aren't modified, consider using Arc<str>.