abi/kern/userlib: Use usize-like Addr in even more places

[jamesmunns]

In #2703, @hawkw (reasonably) asked "Why is X not also an Addr". The answer is "wow it touched a lot more stuff", but I think is still the right choice.

So: I have made this a PR to the other PR to make the concrete diff of the new-new changes easier to review.

These changes should be treated with great suspicion, they are extremely load bearing.

[hawkw]

yeah okay that's a a bunch of stuff, but i think this is good!

[jamesmunns]

In case you wondered, "will this make humility mad?" The answer is yes, undoubtedly:

jamesmunns@lurch ~ $ pfexec ./humility0623 -a /staff/jamesmunns/sidecar-b-abi.zip -t sidecar-sp tasks
humility: WARNING: archive on command-line overriding archive in environment file
humility: attached to 0483:374e:0028001E4741500720383733 via ST-Link V3
system time = 57185
ID TASK                       GEN PRI STATE    
 0 jefe                         0   0 recv, notif: fault timer(T+15)
humility tasks failed: loading reflected value of type humility_doppel::TaskDesc

Caused by:
    not a base type: Tuple(Tuple("Addr", [Base(U32(134790657))]))