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>

tests/functional/binary-cache.sh

@@ -70,7 +70,7 @@ export _NIX_FORCE_HTTP=1
 basicDownloadTests
 
 
-# Test whether Nix notices if the NAR doesn't match the hash in the NAR info.
+# Test whether Lix notices if the NAR doesn't match the hash in the NAR info.
 clearStore
 
 nar=$(ls $cacheDir/nar/*.nar.xz | head -n1)