Smaller, faster cache downloads with LZFSE compression and cache version 6

Remote cache artifacts are now compressed with AppleArchive/LZFSE instead of being stored as uncompressed ZIPs, which makes cold cache downloads roughly 76% smaller (a 2.45 GB cache dropped to about 0.54 GB in Tuist’s benchmarking) while also compressing and decompressing far faster. Because AppleArchive is a new format, the cache version was bumped to v6, so existing caches will need a one-time re-warm on upgrade to this CLI. The same change also fixes a concurrency bug where concurrent uploads of cache items that shared a hash but had different names could race on the same temporary archive path and upload a truncated or wrong artifact; download paths were already safe.