Reconsider shippable flag effect

[SamBrishes]

Just investigated further and it seems that disabling the "shippable" flag still applies shipping costs to the order. That shouldn't happen, right?

So both in the cart and in the quickcheckout I see the default shipping method price added to the total. And the shipping method selector is present.

Variants or no variants: the issue seems to persist.

When I go over the code, I see that only the is_virtual flag is used not to unset the shipping method. Is this something we can change?

Originally posted by @chocolata in #600 (comment)

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Could we also review the functionality of the "shippable" flag? My clients are finding it unclear when to select this option, particularly for events or memberships. Despite unchecking the "shippable" option, the checkout process still includes shipping costs. It appears that only the "is_virtual" flag exempts an item from shipping charges, which seems counterintuitive. Could we have a look at this behavior and see if it would be beneficial to change it?

Originally posted by @chocolata in #600 (comment)