Booster: Add internalised representations for Int and Bool

[jberthold]

PR #3828 adds hooks for Int and Bool sorted values that currently require frequent conversions from domain values to the internal types Integer and Bool (see #3828 (comment))

We should test an implementation that internalises these two sorts to avoid the conversion overhead.

If/when further hooks for other primitive types (String, Bytes) are implemented, they should likewise be internalised.