perf: cache module flags in symbol plists

For small amounts of data, symbol plists are the most efficient (space
and time wise) as data access gets in Emacs. Hash tables, though O(1),
impose a minimum threshold of overhead before it becomes the efficient
option, but this benefit won't be obvious for datasets of at least 60 or
less.

Since modulep! is used *a lot*, and used to determine a module's
state (and state of its flags), there is a benefit to caching it.
Still, this is only a read-only cache, and does not replace the
`doom-modules` hash-table, which will always be the preferred interface
for the rest of the module API.

lisp/cli/autoloads.el

@@ -47,6 +47,12 @@ hoist buggy forms into autoloads.")
          (cl-loop for var in doom-autoloads-cached-vars
                   when (boundp var)
                   collect `(set ',var ',(symbol-value var)))
+         ;; Cache module state and flags in symbol plists for quick lookup by
+         ;; `modulep!' later.
+         (cl-loop for (category . modules) in (seq-group-by #'car (doom-module-list))
+                  collect `(setplist ',category
+                            (quote ,(cl-loop for (_ . module) in modules
+                                             nconc `(,module ,(get category module))))))
          (doom-autoloads--scan
           (append (doom-glob doom-core-dir "lib/*.el")
                   (cl-loop for dir