nix: rename custom -> packages

nix/packages/altiosevka/buildplan.toml

@@ -0,0 +1,26 @@
+[buildPlans.altiosevka]
+family = "iosevka"
+spacing = "term"
+serifs = "sans"
+noLigation = true
+
+[buildPlans.altiosevka.variants.design]
+capital-z = 'straight-serifless-with-crossbar'
+capital-q = 'crossing'
+lower-lambda = 'tailed-turn'
+seven = 'straight-serifless-crossbar'
+number-sign = 'slanted'
+ampersand = "et-tailed"
+dollar = 'open'
+cent = "open"
+percent = 'rings-continuous-slash-also-connected'
+# explicitly declare with-notch
+lig-equal-chain = 'with-notch'
+lig-hyphen-chain = 'with-notch'
+lig-plus-chain = 'with-notch'
+lig-double-arrow-bar = 'with-notch'
+lig-single-arrow-bar = 'with-notch'
+
+[buildPlans.altiosevka.variants.italic]
+v = "cursive-serifless"
+w = "cursive-serifless"

nix/packages/altiosevka/default.nix

@@ -0,0 +1,17 @@
+{ iosevka }:
+let
+  pname = "altiosevka";
+in
+(iosevka.overrideAttrs (_: {
+  inherit pname;
+})).override
+  {
+    set = pname;
+    /*
+      Guide: https://github.com/be5invis/Iosevka/blob/main/doc/custom-build.md
+
+      Use `term` spacing to avoid dashed arrow issue
+      https://github.com/ryanoasis/nerd-fonts/issues/1018
+    */
+    privateBuildPlan = builtins.readFile ./buildplan.toml;
+  }