Update makepkg & pacman config inline with upstream v7

[alexheretic]

• Add v7 pacman conf defaults, including DownloadUser = alpm
• Remove devtools zstd compression defaults
• Enable ParallelDownloads = 5 by default as it is just better
• Include "RUST LANGUAGE SUPPORT" section directly as I'm not sure exactly how "/etc/makepkg.conf.d/*.conf" files work with the custo chroot makepkg.conf file.

[AladW]

Note that systemd-nspawn doesn't support landlock for some reason, so DisableSandbox is also needed for now.

[alexheretic]

Note that systemd-nspawn doesn't support landlock for some reason, so DisableSandbox is also needed for now.

I see this caused error: restricting filesystem access failed because landlock is not supported by the kernel! log but builds still seemed to continue.

I'll change the default thanks for pointing that out!