feat(network): limit concurrent network requests

[KSXGitHub]

Fix the "too many open files" error.

Closes #116

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (9a949c1) 87.02% compared to head (66ee2df) 87.04%.
Report is 3 commits behind head on main.

Files	Patch %	Lines
crates/network/src/lib.rs	95.23%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #210      +/-   ##
==========================================
+ Coverage   87.02%   87.04%   +0.02%     
==========================================
  Files          56       57       +1     
  Lines        2828     2848      +20     
==========================================
+ Hits         2461     2479      +18     
- Misses        367      369       +2     

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[github-actions]

Micro-Benchmark Results

Linux

group                          main                                   pr
-----                          ----                                   --
tarball/download_dependency    1.01      6.7±0.21ms   647.1 KB/sec    1.00      6.7±0.21ms   651.5 KB/sec

[github-actions]

Integrated-Benchmark Report (Linux)

Scenario: Frozen Lockfile

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
pacquet@HEAD	130.6 ± 5.9	119.6	139.2	1.00
pacquet@main	136.7 ± 10.9	123.7	162.4	1.05 ± 0.10

BENCHMARK_REPORT.json

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[KSXGitHub]

@zkochan I have tested this with a very big lockfile (which was generated from the alotta-files fixture) and see that it does emit any error while main still crashes with "too many open files". That is to say, this PR fixes the problem. Now, I want to ask if you want to add that big lockfile to the test?

[zkochan]

The big lockfile that I used for testing is created by this package.json: https://github.com/pnpm/pnpm.io/blob/main/benchmarks/fixtures/alotta-files/package.json