Refactor: improve quality, fewer calls to fs.statSync

[sgb-io]

• Refactored core logic to remove some un-neccessary calls to fs.statSync (we already had the data in the logic)
• Split apart util into smaller, focused utils
• Move some top level code into utils
• Relocated a type into the types file
• Reduced some duplication around excluding directories/files
• Simplified logic around dot files / dirs. Also patched a missing case from before, although I have not tested this before/after the change.

New codehawk scores:

• Average: 54.30 => 56.28 (+1.98)
• Worst: 45.24 => 46.65 (+1.41)

Relevant to #85