fix: wait for the zip module to load before traversing in folders:download --zip

[dgilman-perplexity]

Fixes #718

What

folders:download --zip regressed in v4.10.0: the archive is left empty (or the command hangs) and the files are written loose to the destination. #686 switched to the ESM-only archiver 8 and made _setupZip() async to await import('archiver'), but run() does not wait for it, so this.zip is still undefined when the first items are processed and they take the non-zip code path.

This change:

• adds _loadZipArchive(), awaited in run() before traversal starts, so the archiver module is loaded up front;
• makes _setupZip() synchronous again, so this.zip is assigned before _getItems() yields the first item (the returned promise still resolves when the output stream closes, as before).

Awaiting _setupZip() itself would deadlock, since its promise only resolves after finalize().

Tests

• New test should initialize the zip archive before traversing the folder: stubs _getItems() and asserts this.zip is already set when it is first called. Fails on main (first --zip download in the process races the dynamic import), passes with this change.
• The existing --zip test now verifies the archive: it lists the central-directory entries (small helper, no new dependency) and checks that nothing was written next to the .zip. This resolves the 2018 @TODO there.
• npm test: 1191 passing, 9 pending. eslint and prettier clean on the touched files.

Reproduced manually on Node 20.20.1 with a mock API: 4.10.0 gives a 0-byte zip plus loose files 5/5; with this patch applied to 4.10.0, 5/5 valid archives. box files:zip is unaffected.

[CLAassistant]

All committers have signed the CLA.

[coveralls]

Coverage Report for CI Build 34503039201

Coverage at 84.916% (no base build to compare)

Details

• Coverage remained the same as the base build.
• Patch coverage: 1 of 1 lines across 1 file are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	6061
Covered Lines:	5396
Line Coverage:	89.03%
Relevant Branches:	2153
Covered Branches:	1579
Branch Coverage:	73.34%
Branches in Coverage %:	Yes
Coverage Strength:	642.63 hits per line

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💛 - Coveralls

[arjankowski]

Thanks for the fix, @dgilman-perplexity!
I've cherry-picked your commit into #721 from an internal branch so that all CI checks (including the FOSSA license scan) can run — fork PRs don't have access to repository secrets, which caused FOSSA to fail here.

Closing this in favor of #721