unpack: open file handle only once

[zkat]

This gives a significant speed boost, specially when doing chown and utimes operations, by reducing the number of fd open+close ops.

Note: this PR is still WIP while I figure out why tests are failing. It looks like error handling needs to change and the stuff you see for handling errors right now is mostly me flopping around trying to figure out the issue.

This PR is inspired by yarnpkg/yarn#4486, which did this for Yarn's own extraction and it had a pretty neat speed boost! 🎉

Benchmarks

Before

benchmarks/extract/node-tar-file-async.js
791.322
844.052
887.71
898.871
924.761
benchmarks/extract/node-tar-stream-sync.js
1089.522
1122.212
1077.03
1045.234
1009.606

After

benchmarks/extract/node-tar-file-async.js
619.741
654.146
638.94
657.804
708.489
benchmarks/extract/node-tar-stream-async.js
793.267
779.895
736.296
718.423
777.464

[isaacs]

Conflicts with fsm update, closing.

[nowakwp]

#420