Update express.ui.hold() to accept any type of object

[wch]

This addresses one of the issues described in #1083.

[wch]

For future reference: The result of ui.hold() is a list. If a RecallContextManager wants to consume the result of a ui.hold(), it could simply use a for loop to iterate over the list:

with ui.hold() as held:
    "a"
    "b"

with ui.card():
    for x in held:
        x

It could also be done in a function like this:

@expressify
def spread(lst: list[object]) -> None:
    for x in lst:
        x

with ui.hold() as held:
    "a"
    " b "

with ui.card():
    spread(held)