Tightening up metering in auth

[jayz22]

What

Fix a few small but protocol-breaking metering issues discovered by the security review:
i. auth entry charging the wrong amount #1297
ii. (not protocol breaking) auth snapshot() function charge after allocation
iii. auth manager not charging RefCell wrapping.

I also did a clean up by wrapping the with_capacity method with metering into a new MeteredContainer::with_metered_capacity method, which makes sure bugs like (i) and (ii) above cannot happen.

Unfortunately these breaks a lot of existing observations that depends on auth, basically all mem_bytes have increased by 8 (size of the RefCell counter) and cpu_insns have increased by 2, which is caused by fixing (iii).

Why

[TODO: Why this change is being made. Include any context required to understand the why.]

Known limitations

[TODO or N/A]

[graydon]

LGTM, thanks!