Arial Black
Adventurer
Actions have not been divisible in 1e, 2e, 3e or 5e except when an exception is made through an item, spell or ability.
This is not true.
In 3e, as soon as swift/immediate actions were introduced, they could be taken at any time on your turn (for swift) and any time at all for immediate.
Free actions were in 3e at its beginning, and you can take them any time on your turn.
A swift action is identical to a free action, except you can only take one swift action per turn.
Swift and free actions certainly can be taken between attacks of a full attack in 3e. It says so in the rules.
It says in the 5e rules that you can take your bonus action, if you have one, at ANY time on your turn. Meanwhile, nowhere does it say that 'actions are indivisible'. You're asserting a 'rule' that does not exist to disregard a rule which does exist!