feat(base): add cursor colors and missing cursor groups

Author: A-Lamia

lua/astrotheme/groups/base.lua

@@ -3,7 +3,9 @@ local function callback()
     Normal = { fg = C.text, bg = C.base },
     NormalNC = { fg = C.text, bg = C.mantle },
     Title = { fg = C.cyan, bg = C.none },
-    Cursor = { fg = C.none, bg = C.none },
+    Cursor = { fg = C.base, bg = C.text },
+    CursorIM = { link = "Cursor" },
+    lCursor = { link = "Cursor" },
     ColorColumn = { fg = C.none, bg = C.overlay1 },
     CursorLineNr = { fg = C.text, bg = C.none },
     Conceal = { fg = C.subtext0, bg = C.none },