feat: reject ZIP archives with unsupported Deflate64 compression up front

[otavio]

Summary

• Adds a ZIP central-directory preflight that scans entries for compression methods libarchive cannot decode (currently just Deflate64 / method 9) and fails fast with a new Error::UnsupportedZipCompression(Vec<(String, u16)>) listing the offending entries.
• Wires the preflight into list_archive_files, uncompress_archive, uncompress_archive_file, and ArchiveIterator so the error surfaces before libarchive aborts mid-stream with Unsupported ZIP compression method (9: deflation-64-bit).
• Replaces AsyncReadWrapper::seek's unreachable!() with ErrorKind::Unsupported so the preflight degrades gracefully on unseekable async readers (channel-fed wrappers) instead of panicking.

Closes #136.

Design notes

• Hand-rolled central-directory parser (~160 LOC, no new deps). Parses classic EOCD and Zip64 EOCD/locator, reads the whole CD in one shot for O(1) syscalls per archive, caps allocation at 16 MiB so a malformed/hostile file can't OOM us. Non-ZIP inputs, malformed ZIPs, and unseekable readers all fall through so libarchive keeps its normal behavior — we only intercept when we are sure the archive contains an unsupported method.
• Error variant is structured (Vec<(String, u16)>) rather than a formatted Error::Extraction(String), so callers can pattern-match on offending entries and their method numbers.
• Encryption is intentionally not flagged. libarchive can decrypt ZIP entries via archive_read_add_passphrase; Support encryption? #82 tracks exposing that from this crate. Blocking encrypted entries now would preempt that work. A comment in is_unsupported_method documents the decision.

Test plan

• New regression tests covering the three public entry points (list_archive_files, uncompress_archive, ArchiveIterator::from_read) on a Deflate64 fixture, plus a guard that plain-Deflate (method 8) archives remain unaffected.
• All 39 existing integration tests pass (including the 10 async ones — they exercise the new AsyncReadWrapper::seek fallback path).
• cargo clippy --all-targets clean with default and async features.

Fixture

tests/fixtures/deflate64.zip (229 B) — generated with 7z a -tzip -mm=Deflate64 over a repeated-string payload large enough that 7-Zip actually picks Deflate64 instead of Store. Confirmed Method = Deflate64 via 7z l -slt.

[coveralls]

Coverage Report for CI Build 24793702738

Coverage increased (+0.09%) to 76.947%

Details

• Coverage increased (+0.09%) from the base build.
• Patch coverage: 34 uncovered changes across 2 files (113 of 147 lines covered, 76.87%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
src/zip_preflight.rs	111	80	72.07%
tests/integration_test.rs	29	26	89.66%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	1900
Covered Lines:	1462
Line Coverage:	76.95%
Coverage Strength:	58.08 hits per line

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💛 - Coveralls