Use modern compression algorithm

In short: Please consider switching to using `xz` archives which uses the `lzma` compression algorithm. By my tests this can reduce total backup size by 30%. At current dumps are stored as zip archives. The old and venerable zip primarily uses the `deflate` compression algorithm from 1990. Zips in theory may optionally support `lzma` but most tooling for it does not, including Info-ZIP (which most Linux distros use) which was last updated in 2008. There is support for `bzip2` in Info-ZIP and while it's better than `deflate`, it's only slightly better. The solution I'm proposing is to switch to a better container with better algorithm support. By my quick tests `xz` is the winner as it uses the `lzma` algorithm with a robust and modern container format. For comparison I've also included the legacy lzma container format below[^1]. There's potentially further gains to be had by increasing the compression factor from the default 6 up to 7..9 but that increases the memory requirements. A 7 might be a good compromise. Sample files, first is dump as stored by pgbackweb, then the same deflated. The rest are different ways of compressing the same dump: > 3.0M dump.sql 319k dump.sql.gz 317k dump-20251226-020000-6cbade9f-0ef5-45cf-9778-9b6aa4dc7d0a.zip 312k dump.sql.zip 307k dump.sql.bz2 277k dump.sql.zst 218k dump.sql.xz 218k dump.sql.lzma The file types of the same tests: > dump-20251226-020000-6cbade9f-0ef5-45cf-9778-9b6aa4dc7d0a.zip: Zip archive data, at least v2.0 to extract, compression method=deflate dump.sql: ASCII text dump.sql.bz2: bzip2 compressed data, block size = 900k dump.sql.gz: gzip compressed data, was "dump.sql", last modified: Sun Dec 30 22:00:00 1979, from Unix, original size modulo 2^32 3004661 dump.sql.lzma: LZMA compressed data, streamed dump.sql.xz: XZ compressed data, checksum CRC64 dump.sql.zip: Zip archive data, at least v4.6 to extract, compression method=bzip2 dump.sql.zst: Zstandard compressed data (v0.8+), Dictionary ID: None [^1]: While technically legacy lzma is the smallest. it's purely by having a smaller header than the modern xz by a couple of bytes. xz is superior in all other ways.