chore: rebrand Nix to Lix when it makes sense

Here's my guide so far:

$ rg '((?!(recursive).*) Nix
(?!(daemon|store|expression|Rocks!|Packages|language|derivation|archive|account|user|sandbox|flake).*))'
-g '!doc/' --pcre2

All items from this query have been tackled. For the documentation side:
that's for https://git.lix.systems/lix-project/lix/issues/162.

Additionally, all remaining references to github.com/NixOS/nix which
were not relevant were also replaced.

Fixes: https://git.lix.systems/lix-project/lix/issues/148.
Fixes: https://git.lix.systems/lix-project/lix/issues/162.
Change-Id: Ib3451fae5cb8ab8cd9ac9e4e4551284ee6794545
Signed-off-by: Raito Bezarius <raito@lix.systems>

src/libstore/linux/fchmodat2-compat.hh

@@ -5,7 +5,7 @@
  * a glibc git checkout via `rg --pcre2 'define __NR_fchmodat2 (?!452)'`.
  *
  * The problem is that glibc 2.39 and libseccomp 2.5.5 are needed to
- * get the syscall number. However, a Nix built against nixpkgs 23.11
+ * get the syscall number. However, a Lix built against nixpkgs 23.11
  * (glibc 2.38) should still have the issue fixed without depending
  * on the build environment.
  *