[move][framework] Clean-ups

[amnn]

Issue tracking various potential clean-ups to the sui framework and move stdlib, such as:

• Merging std::address and `sui::address
• Adding a module per numeric type instead of a catch all math.move
• Standardising the offering of math APIs across all types.

[stefan-mysten]

@amnn Is the content of this issue still valid or can we close it?

[amnn]

Some of it still applies, like offering a module per numeric type and some standardised math libraries, but the best people to ask are the folks who are closest to that codebase, e.g. @damirka and maybe @healthydeve for the DeFi angle.