Fixes implicit folder detection

[arcanis]

Zip archives may have directory entries baked within the archive:

        0  06-22-1984 21:50   node_modules/
        0  06-22-1984 21:50   node_modules/left-pad/
      646  06-22-1984 21:50   node_modules/left-pad/package.json
        0  06-22-1984 21:50   node_modules/left-pad/perf/
      216  06-22-1984 21:50   node_modules/left-pad/perf/es6Repeat.js

Or they may be missing:

      646  06-22-1984 21:50   node_modules/left-pad/package.json
      216  06-22-1984 21:50   node_modules/left-pad/perf/es6Repeat.js

In that second case we try to normalize the archive so that in both cases we end up with ["node_modules/", "node_modules/left-pad/", "node_modules/left-pad/perf/"] in the dirs set. Unfortunately the logic is bogus and we're not going over the very last component; so in this case, we would be missing the node_modules/left-pad/perf/ entry.

This is then causing issues when the package has a package.json in said directory, which happens for example for underscore (it contains a node_modules/underscore/modules/package.json file with "type": "module").

This PR fixes the issue and adds new tests.

[github-actions]

Benchmark for d6764b0

Click to view benchmark

Test	Base	PR	%
vpath_edge_cases	2.7±0.08µs	2.8±0.30µs	+3.70%
vpath_mixed_workload	4.9±0.19µs	4.8±0.16µs	-2.04%
vpath_native	1566.2±72.80ns	1563.3±68.31ns	-0.19%
vpath_virtual	3.6±0.11µs	3.6±0.18µs	0.00%
vpath_virtual_zip	2.9±0.08µs	2.9±0.10µs	0.00%
vpath_zip	2.0±0.08µs	2.0±0.12µs	0.00%

[github-actions]

Benchmark for 2943924

Click to view benchmark

Test	Base	PR	%
vpath_edge_cases	2.8±0.16µs	2.7±0.16µs	-3.57%
vpath_mixed_workload	4.9±0.44µs	4.8±0.24µs	-2.04%
vpath_native	1576.9±145.60ns	1583.6±108.50ns	+0.42%
vpath_virtual	3.6±0.21µs	3.6±0.17µs	0.00%
vpath_virtual_zip	3.0±0.17µs	2.9±0.14µs	-3.33%
vpath_zip	2.1±0.16µs	2.1±0.13µs	0.00%