Box {Component,Modal}Interaction::member

[DPlayer234]

To match what has been done to CommandInteraction in the past and actually make its size reduction useful for Interaction (again?).
Also reduces the size of Event.

64-bit app type sizes without this PR:

ComponentInteraction: 1120 bytes
ModalInteraction: 1096 bytes
Interaction: 1120 bytes
Event: 1120 bytes

With this PR:

ComponentInteraction: 768 bytes
ModalInteraction: 744 bytes
Interaction: 792 bytes
Event: 792 bytes

[DPlayer234]

With this PR, the size difference for the variants within Event is apparently no longer above the threshold to fire clippy::large_enum_variants. Since this repo also lints on allow, I opted to remove the expect entirely.