feat(recipes): add recipe for caching colorscheme settings

Author: mehalter

lua/astrocommunity/recipes/cache-colorscheme/README.md

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+# Cache Colorscheme
+
+**Website:** <https://docs.astronvim.com/recipes/colorscheme/#cache-colorscheme>
+
+This plugin specification caches the last chosen colorscheme by the user to persist colorscheme changes without modifying user configuration.

lua/astrocommunity/recipes/cache-colorscheme/init.lua

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+-- pick a location to cache colorscheme
+local colorscheme_cache = vim.fs.joinpath(vim.fn.stdpath "state" --[[@as string]], "last_colorscheme")
+
+--- Execute function with open file
+---@param file string path to file to interact with
+---@param mode openmode the mode in which to open the file
+---@param callback fun(fd:file*) the callback to execute with the opened file
+---@param on_error? fun(err:string) the callback to execute if unable to open the file
+local function with_file(file, mode, callback, on_error)
+  local fd, errmsg = io.open(file, mode)
+  if fd then
+    callback(fd)
+    fd:close()
+  elseif errmsg and on_error then
+    on_error(errmsg)
+  end
+end
+
+return {
+  {
+    "AstroNvim/astroui",
+    --@param opts AstroUIOpts
+    opts = function(_, opts)
+      -- read colorscheme cache on open
+      with_file(colorscheme_cache, "r", function(file) opts.colorscheme = file:read "*a" end)
+    end,
+  },
+  {
+    "AstroNvim/astrocore",
+    ---@type AstroCoreOpts
+    opts = {
+      autocmds = {
+        -- save colorscheme to cache on change
+        cache_colorscheme = {
+          {
+            event = "ColorScheme",
+            callback = function(args)
+              if args.match then with_file(colorscheme_cache, "w+", function(file) file:write(args.match) end) end
+            end,
+          },
+        },
+      },
+    },
+  },
+}