fast-scan: Apply performance improvements

[pombredanne]

After running and profiling, we will find opportunities to speed up the code and should apply performance improvements. The goal is to resolve issues impeding performance discovered during the scan benchmarks for license, copyright, and package detection and the profile hotspots performances. The exact optimisations that will be performed will depend on results of the benchmarks of course and will be detailed as we go:

• fast-scan: Apply performance improvements to code: batch 1 (copyright or from benchmark results) #4063
• fast-scan: Apply performance improvements to code: batch 2 (file system walking or from benchmark results) #4064
• fast-scan: Apply performance improvements to code: batch 3 (archive extraction or from benchmark results) #4065
• fast-scan: Apply performance improvements to code: batch 4 (from benchmark results) #4066
• fast-scan: Apply performance improvements to code: batch 5 (from benchmark results) #4067
• fast-scan: Apply performance improvements to code: batch 6 (from benchmark results) scancode.io#1501