feat: add exact match comparator

[ruslanSorokin]

No description provided.

[ruslanSorokin]

Implements #1085

[ruslanSorokin]

I'm certain that the keyword is always truncated by one character on the right, but I'm not sure if I'm fixing it in the right place. I would appreciate it if you could take a look at this with your understanding of the code's semantics as its author.

[Saghen]

Thanks for looking into this. We should calculate whether the match is exact during the fuzzy matching, since the keyword range can vary depending on the item, so this change isn't trivial: https://github.com/Saghen/blink.cmp/blob/main/lua/blink/cmp/fuzzy/fuzzy.rs#L79

I believe we should add an exact property on the matched item in frizbee, since it's already calculated there. We currently give a score bonus of 4 in this case, so this issue seems to only appear when users change their score_offset: https://github.com/Saghen/frizbee/blob/main/src/simd.rs#L247. We would need to make sure this doesn't affect performance as well