Allow Everbook to handle sub-iotas in non-lists

[kineticneticat]

Changes getNestedIota to check for subiotas rather than just for list iotas
Adds an interface to allow addons to handle iota replacement

[object-Object]

One minor javadoc suggestion, but the code itself looks fine to me.

However, can you add a couple of unit tests? See here for an example of the setup required to instantiate iotas in a unit test (you'll need to merge or rebase onto the new commits from main):

Hexal/Common/src/test/java/ram/talia/hexal/api/everbook/FileEncrypterDecrypterTest.kt

Lines 66 to 77 in 8a61a28

	companion object {
	@BeforeAll
	@JvmStatic
	fun setUpOnce() {
	// hack: we don't need bootstrap to succeed, we just need to set isBootstrapped so we can create registries
	try {
	Bootstrap.bootStrap()
	} catch (_: Throwable) {}
	HexIotaTypes.registerTypes { t, id -> Registry.register(HexIotaTypes.REGISTRY, id, t) }
	}
	}

[object-Object]

Merging without the unit tests so we can get this released.