Adds support for Fossil SCM source tree archives as zig build dependencies

[cipharius]

Fossil SCM can generate tar.gz compressed source tree archives at any given artifiact, which aligns well with zig build dependency fetching system.

Problem is that fossil serves these archives with mime type application/x-compressed. While it's too generic, zig should accept it nonetheless, but fall back to filename parsing to determine source archive type.

Other problem is that fossil generates tar archives where directory headers don't have trailing slash which causes issues with the way how std/tar.zig parses archive paths.

[cipharius]

This also potentially resolves #17779 and #17620.

Seems pretty likely, that the archives in these issues also have directory paths without trailing slashes. Otherwise, if regular file path will get stripped too much, the BadFileName error will be raised instead.

Edit:
Seems like in #17620 case it would still be an error, because zig expects the archive to have root directory, which is a good style for source archives. The case of missing root directory in tar archive would have to be handled separately

[nektro]

has it been reported to fossil how wrong application/x-compressed is? I think there should be a tracking issue linked if this change makes it in

[cipharius]

Seems like it wasn't given much thought, perhaps back when this was implemented application/x-compressed seemed fine.

https://fossil-scm.org/home/info/d5d676f0c7f37d6b

[andrewrk]

Thanks for the contribution. I'm happy to accept this patch. Would you mind rebasing it on the latest master branch code? The changes to std.tar might not be necessary anymore since d55d1e3.

[cipharius]

Tested the std.tar change, still relevant. It makes it a non-error if too much is stripped from tar path, it returns empty string. Since the stripComponents is a local function, such solution seems alright.

[andrewrk]

Thanks for the rebase and re-testing. Nice patch 👍