memory: handling of `lru_cache`

[adbar]

See discussions in https://github.com/adbar/htmldate/issues/56 and https://github.com/adbar/htmldate/issues/57.

[adbar]

• [x] check all functions using such a cache
  • [x] in trafilatura, htmldate and courlan
  • [x] in all the underlying libraries
• [x] write a reset_caches() function which calls function_name.cache_clear() on all concerned functions

[adbar]

After installing the latest version straight from the repository, the new function can be called as follows whenever one sees fit, for example every n URLs:

from trafilatura.meta import reset_caches

# at any given point
reset_caches()