This branch is to prepare for small fields. Specifically, to fix things that absolutely must be fixed before we can use small fields:

• (Unchecked Lookups) The use of :unchecked lookups into zkasm modules is problematic for small fields. This simply updates all relevant lookups into zkasm modules to be checked, adding casts as necessary.
• (Bombs) hub mxp oob (noting that oob remains an issue and will be fixed separately)
• (Irregular Selector) romlex selector has two limbs

Bombs

• hub takes ??? to split
• mmio takes 29s to split
• mxp takes 15s to split
• oob takes ??? to split