Replace use of LRU package with a package with permissive license

Hello! It is in my interest to replace the use of the following LRU cache with one that comes from a package with a permissive license: https://gitlab.com/cznic/gc/-/blob/master/v3/gc.go?ref_type=heads#L74

The package in question uses a Mozilla Public License 2.0 which requires the disclosure of the source code of any binary distributed which contains this. This is problematic for companies wanting to use software that includes modernc.org software since it would require them to release their source code and give up their competitive advantage.