Add helpers for container bulk init; applies to auth metering

[jayz22]

What

Resolves #668

• Close metering gaps in Auth-related code. Mostly around unmetered container usages i.e. Vec<T>.
• Added a couple of helper traits MeteredContainer, MeteredCollect to make the bulk collection with metering a little bit more seamless.

Why

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

Known limitations

[TODO or N/A]

[dmkozh]

This looks nice, thanks! I think that's much better than just using metered vector internally at cost of n^2 memory and allocations.