Investigate using git-restore-mtime package for cacheing

Problem/Motivation

Caching for cspell uses content caching strategy right now. This is good, but means hashing all files. We could investigate using the git-restore-mtime package. This will set mtime to the git history and could mean we can use the metadata cachings strategy. This *might* improve the runtimes even more.

https://stackoverflow.com/questions/2458042/restore-a-files-modification...

Quick testrun of impact of running git restore-mtime:

[32;1m$ git restore-mtime[0;m
18,163 files to be processed in work dir
Statistics:
         0.22 seconds
       18,421 log lines processed
           50 commits evaluated
        4,057 directories updated
       18,163 files updated

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet