Revert "Rework definition of HT to not include halting. This makes things more complicated, tbh."

This reverts commit ba51deba312e2729229641d66c1ca5e5d997517c.
Add a comment back from the reverted lhs-halt stuff.
Drop step-app-r.
Make everything deterministic.
Prove that the semantics are deterministic.
Add some stuff for equivalence.
Generalize a proof a bit more.
Generalized it a bit. Move contexts to a new file.
Woo, generalize
Add thing for congruence.
Stop using numerals and exists for kleene. Use a custom record with val.
Prove that obs equiv is a congruence
Definte consistency.
Show observational equivalence is the coarsest consistent congruence.
Define open logical equivalence.
Prove the easy properties.
Prove refl.