Replace Set object with Map object

[mateonunez]

I was working on #12 and #13. I stashed my code a lot of times looking to keep the same architecture of inserted documents. So hard or stressful for Lyra.

I created a new architecture for inserted documents, replacing the Set with a Map<string, number> (where the number could be replaced with a typed object that will contain metadata).

The tests are awesome:

main branch:

with new implementations:

The elapsed time was computed before the insert and after the search methods. I've inserted 1000 documents.

This could be an idea to implement more metadata when a document is indexed.

I also created a branch (in WIP and breaking in some cases) to show how could it work.

[mateonunez]

I've fixed some tests in the branch (still in WIP). I also did some benchmarks.

feat/occurrences-sort benchmark (replaced 'cause checkout on the wrong branch):
https://pastebin.com/raw/90V6r1ZL

main benchmark
https://pastebin.com/raw/u4ARt3us

I think this implementation can work properly, it doesn't have a big impact on indexing or searching performance, and also could bring an extension toward the functionality that will be able to be performed by Lyra. For example, we can implement a metadata object. I also created a branch to show you how it could work.

[micheleriva]

@mateonunez as wrote in https://github.com/nearform/lyra/discussions/56, we had to remove all the Map objects to perform dpack serialization on the indexes. As for now, it is not possible to add more Map objects to the codebase 😞