Evaluate all Vec usage and replace with SmallVec where apropriate

[bluejekyll]

Make sure to run benchmarks before and after to see if there is a difference ;)

This should reduce heap allocations throughout the various libraries.

[link2xt]

For some reason there is also a tinyvec dependency already. tinyvec is a safer alternative to smallvec:
https://www.reddit.com/r/rust/comments/n2429h/arrayvec_vs_smallvec_vs_tinyvec/

Which one to use depends on actual performance of course, but would be nice to choose one and have a single dependency.

[djc]

See some discussion in #1388.

If you want to rip out uses of smallvec in favor of tinyvec, that'd be great!

[darnuria]

Hi @bluejekyll /@djc, have some time this end of the month if still pertinent i can try to claim the task and do something to only use tinyvec ! :)

(maybe a renaming of the ticket or opening a new one if neccessary)