Optimize side table masks

[zhouwfang]

Based on experiments, these are the smallest masks to pass CI. In other words, SideTableEntry only requires u35 at this point. I'll add the fields from func_type() and func() in module.rs to the side table in #711, and SideTableEntry as u64 might not be sufficient.

#46

[ia0]

That's most probably too strict on the counts. I think we should eventually end up with:

• 16 bits delta IP
• 16 bits delta STP
• 4 bits val count
• 12 bits pop count

This gives 48 bits aligned on 16 bits.