Select caching decorator based on run state

[lunkwill42]

This introduces a new lru_cache decorator that will change its behavior according to the current environment.

If imported in isolation, it selects the functools.lru_cache implementation. If imported in a fully integrated system (ie. Redis connection settings are available), the RedisLRU cache implementation is used.

[codecov[bot]]

Codecov Report

Merging #235 (38fd256) into develop (45e0207) will increase coverage by 0.04%. The diff coverage is 88.00%.

@@             Coverage Diff             @@
##           develop     #235      +/-   ##
===========================================
+ Coverage    59.64%   59.69%   +0.04%     
===========================================
  Files           62       63       +1     
  Lines         6218     6233      +15     
===========================================
+ Hits          3709     3721      +12     
- Misses        2509     2512       +3     

Impacted Files	Coverage Δ
src/cnaas_nms/db/cache.py	84.21% <84.21%> (ø)
src/cnaas_nms/db/settings.py	81.08% <100.00%> (-0.20%)	:arrow_down:

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[lunkwill42]

This has actually been made redundant/obsolete by #245 - thanks @pboers1988 !