[Modules] Module cache

[Xavier D. <xav...@gm...>]

Hello All,

Happy `module switch year/2023` everyone.

Work on next version (5.3) has started some weeks ago. First feature
finished is the module cache mechanism:

  https://modules.readthedocs.io/en/latest/MIGRATING.html#module-cache

A cache file can be built under each modulepath with new `cachebuild`
sub-command. When available, it is used by module search mechanism
rather walking through modulepath directory. I/O operations are saved
and processing time is reduced.

Options are available to optimize cache read/write buffer size
(cache_buffer_bytes), ignore cache file (--ignore-cache) and expire
cache file (cache_expiry_secs).

Regards,
Xavier