Rework Rust runtime and builder

[ecklf]

This PR reworks the builder and runtime to support the latest AWS lambda runtime which changed almost everything. Examples can be found in the examples folder.

Optimizations that will be considered in follow-up PRs:

• Improve build caching by looking at https://github.com/Swatinem/rust-cache.
• Merge handlers into one lambda. Build scripts might be a good solution for that.
• CI setup

[abcd-ca]

Just did a quick smoke test. Much better, good job, thanks!