transient--parse-suffix: Fix regression breaking :setup-children

In [1: fb88f80] we wrongly concluded that the only type of function
left to be handled by this branch are `lambda' expressions.  While that
is true during macro-expansion, this function may also be called from a
prefix's `:setup-children' function, in which case we also have to deal
with byte-code function objects and compiled functions.

So go back to handle everything for which `commandp' returns non-nil,
except for strings, which Transient does not support as commands.

Because none of command types supported here have to be quoted, we can
keep the part of [1: fb88f80], which stopped using `macroexp-quote'.

Closes #313.
Closes tarsius/notmuch-transient#2.

1: 2024-09-02 fb88f80
   transient--parse-suffix: Clarify clause, removing dead code

CHANGELOG

@@ -1,4 +1,12 @@
 # -*- mode: org -*-
+* v0.7.7    UNRELEASED
+
+Bug fix:
+
+- Fix a regression introduced by the previous commit, which broke
+  dynamic prefixes that use a ~:setup-children~ function to prepare
+  their suffixes.  #313
+
 * v0.7.6    2024-10-01
 
 - ~transient-active-prefix~ now accepts a single prefix symbol, in place

lisp/transient.el

@@ -1187,8 +1187,13 @@ commands are aliases for."
         (error "Need command, argument, `:info' or `:info*'; got `%s'" car))
        ((symbolp car)
         (setq args (plist-put args :command (macroexp-quote pop))))
+       ;; During macro-expansion this is expected to be a `lambda'
+       ;; expression.  When this is called from a `:setup-children'
+       ;; function, it may also be a byte-code function object or a
+       ;; compiled function.  However, we never treat a string as a
+       ;; command, so we have to check for that explicitly.
        ((and (commandp car)
-             (eq (car-safe car) 'lambda))
+             (not (stringp car)))
         (let ((cmd pop)
               (sym (intern
                     (format