refactor: Use haumea for filesystem-based module system for flake outputs

refactor: Use hyphen(`-`) for variable names & folder names(except Python), replace all unserscore(`_`) with hyphen(`-`).

home/darwin/core.nix

@@ -1,3 +1,3 @@
-{username, ...}: {
-  home.homeDirectory = "/Users/${username}";
+{myvars, ...}: {
+  home.homeDirectory = "/Users/${myvars.username}";
 }

home/darwin/ssh.nix

@@ -1,3 +1,3 @@
-{vars_networking, ...}: {
-  programs.ssh.extraConfig = vars_networking.ssh.extraConfig;
+{myvars, ...}: {
+  programs.ssh.extraConfig = myvars.networking.ssh.extraConfig;
 }