Use BitMaps to validate multiple types

[macisamuele]

The goal of this PR is to improve memory utilisation of MultipleTypesValidator as well as improving validation performance.

The validation performance is achieved by:

• replacing iteration over a Vec instance (data are into the heap) with bit operations
• ensuring that errors are as small as possible

Performance improvements have been measured by running the following

rm -rf target/criterion
git co -f 4cf7d8d
cargo bench "type_multiple"
git co -f 9437e9d
sleep 60  # To allow cooling down the laptop
cargo bench "type_multiple"

The raw output is available here
Summary:

• ~21% improvement in compile time
• at least 12% improvement in validation time (it goes up to 34% as well)

NOTE: I've run a subset of benchmarks only selecting the relevant to multiple types

[Stranger6667]

Thank you Samuele!
It is an ingenious trick and I like it a lot :) Great!

What do you think if we can apply it somewhere else as well?

[macisamuele]

I've noticed this "easy win" while working on maci-split-validators.
The branch is far from been really presentable (meant to provide a possible solution for #63)

[Stranger6667]

Cool! Looking forward to seeing a pull request :)