Fix &b crash with input arrivals after save

[Zhou-Yilong]

Fix a segfault in &b after save.

save evaluates mapped delay and initializes the network timing manager.
After strash, &get -nm transfers this timing information into Gia_Man_t::vInArrs. Gia_ManAreaBalance() then writes CI levels through p->vLevels, but the vInArrs branch did not allocate this vector.

Minimal reproducer:

read <library>
read_lib <library>
read i10.aig
strash
map; save; strash
&get -nm; &b

Without save, the sequence completes. Before this fix, the sequence with
save segfaults at src/aig/gia/giaBalAig.c:1064.