fix: improve pack performance by not reading into memory

[BridgeAR]

The current implementation is very slow due to having to load all into memory before writing the file. Pacote itself has a command that does that right away as a stream. This improves the performance significantly.

Fixing the test case seemed more tricky than the fix, so I hope you could suggest what to do about the test.

[wraithgar]

The reason the test fails is because the code is failing. The file is created but it's empty. npm crashes when lib/commands/pack.js tries to run getContents on the returned object, which is no longer a stream.

pacote.tarball.file eventually returns from #toFile:

{
  integrity: 'sha512-...',
  resolved: '/path',
  from: 'file:/path'
}

via

      writer.on('close', () => res({
        integrity: this.integrity && String(this.integrity),
        resolved: this.resolved,
        from: this.from,
      }))

Instead of the tarballStream.

[BridgeAR]

I believe the issue is around the return of the pack call. I do not think it should return the tarball in memory, which is a breaking change for this module. Right now, the PR is definitely incomplete. I think it would just be good to have a closer look and see if we could prevent the in memory read.