rewrite unforkify

hercules_ir/src/ir.rs

hercules_opt/src/editor.rs

hercules_opt/src/fork_guard_elim.rs

hercules_opt/src/forkify.rs

hercules_opt/src/ivar.rs

hercules_opt/src/lib.rs

hercules_opt/src/loop_canonicalization.rs

hercules_opt/src/unforkify.rs

hercules_test/hercules_interpreter/src/interpreter.rs

hercules_test/hercules_interpreter/src/lib.rs

hercules_test/hercules_interpreter/src/value.rs

hercules_test/hercules_tests/tests/fork_transform_tests.rs

hercules_test/hercules_tests/tests/forkify_tests.rs

hercules_test/hercules_tests/tests/interpreter_tests.rs

hercules_test/hercules_tests/tests/loop_tests.rs

hercules_test/test_inputs/3d_fork.hir

hercules_test/test_inputs/forkify/merged_phi_cycle.hir

hercules_test/test_inputs/forkify/split_phi_cycle.hir

...inputs/loop_analysis/alternate_bounds_use_after_loop2.hir

...test/test_inputs/loop_analysis/do_while_separate_body.hir