cache line ranges of chunks for fast lookup

[drahnr]

Is your feature request related to a use-case? Please describe.
Currently performance of #74 is far from acceptable, taking multiple seconds to complete for a small~ish codebase.

Describe the solution you'd like
The majority added delay comes from parsing CheckableChunk over and over again in order to convert ranges to spans and vice versa.

Describe alternatives you've considered
Not really many other options here, we need to get rid of the O(n) and make it a O(1) or O(log n) at least.

[drahnr]

@laysauchoa would you be interested in looking into this? Or do you fancy another issue?