Add support to zstd compress vmtar file

[william-billaud]

• Add support to zstd compressed vmtar files (and XZ, as fsutil.open_decompress is now used to manage decompress)
• Use VmtarFilesystem inside esxi._os, instead of manual tar uncompress
• Add the backport.zstd dependency. In Python 3.14 zstd as been added to standard library (pep-0784), author as backported the lib.
  • Using this lib, we do not need to fully read data in memory when uncompressing zstd, which is more convenient.
• Add an UncompressionError, mainly raised when required dependency is missing. This allows logging when a file couldn't be decompressed due to an error/missing deps
• Initially, using zstandard I encounter uncompression Errors of few zstd file, but this error is not present using backport.zstd (and files from "faulty" archive are present when mounting the disk).
• Add test regarding a zstd compressed vmtar file.

Some note regarding somme "issues" I found into the code

• Perhaps zstandard usage should be fully replaced by backport.zstd/zstd in a dedicated issue
• Perhaps a decompression error should be generated whenever a compressed stream is detected using open_decompress, but the required library is not present (or when decompression has failed). This would warn the user of something abnormal without causing a crash.

I can provide an esxi 8 and esxi 9 disk (30Go, less than 1Go compressed) if needed for testing purposes.

close #1296