Make parsing more performant

[eric-nguyen-cs]

Now

Currently, it takes a few seconds to import some taxonomies and some taxonomies are not parsed before the http requests timeouts.
The parsing step takes too much time

Goal

Understand why parsing takes so much time to respond and resolve it

• Make the parser faster if possible
• If not possible, respond to the client asynchronously

[alexgarel]

@eric-nguyen-cs it's mandatory to make the client respond asynchronously, (there are huge taxonomies). see #206

But working on parsing performance is also important as I believe there might be low hanging fruit.