[mielverkerken]

Summary

Add ZIP64 footer writing support for archives that exceed classic ZIP end-of-central-directory limits.

Previously, creating an archive with more than 65,535 entries fails while writing the classic EOCD record because entry counts are stored as UInt16 values. This change writes ZIP64 end records when needed and keeps the classic EOCD compatibility record with saturated placeholder values.

Changes

• Add a writeBigUInt64LE utility alongside the existing ZIP64 read helper.
• Emit ZIP64 end of central directory record and locator when entry count, central directory size, or central directory offset exceeds classic ZIP limits.
• Preserve the existing classic EOCD output path for small archives.
• Ensure ZIP comments are copied to the correct footer position when ZIP64 records are present.
• Add regression coverage for archives with more than 65,535 entries.

Test Plan

• npm test

Result: 93 passing

[mielverkerken]

#320