The book unlocks are purely based on advancements, which means you could probably do it with just a data pack somehow. (At least judging by what Vanilla Tweaks can do with just data packs.)
The summoning ritual itself is hard-coded with a couple requirements for the arena:
- a beacon block in the middle
- four Gaia Pylons in the corners of a 9x9 block square, one layer above the beacon
- solid ground 1 and/or 2 blocks below the beacon block within a horizontal radius of 12 blocks (euclidean) around the beacon
- 5 blocks of vertical clearance above the arena floor, starting at beacon height
- the arena floor/clearance check ignores the pylon columns of blocks
The arena check is currently not exposed as an API, so even Java code would not really allow you to properly reuse it in an easy way. (We'll probably fix that for later Minecraft versions in some way, so other mods can perform or maybe even modify the test themselves.)