Update ExprLeashHolder to use Leashable instead of LivingEntity

[georgereuben]

Problem

Currently none of the Leash related syntax work with boats meaning you will have to use Reflect and paper syntax instead.

Solution

Updated ExprLeashHolder and EffLeash to use Paper's Leashable instead of the LivingEntity interface.

Testing Completed

Tested with quickTest, skriptTest and Junit tasks

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Completes: #8239

[zspitzer]

@micstriit loader changes suck i know....

[michaeloffner]

make sure this is backward compatible, existing archives containing Lucee bytecode most likely will no longer work with this change.