[fix] Failed to import gptcache due to missing redis dependency

[a9raag]

resolves #521

Moved RedisCacheEviction to its own module to avoid calls that tries to import and install redis

[codecov]

Codecov Report

Merging #522 (09bda62) into dev (790e9f4) will increase coverage by 0.00%.
The diff coverage is 92.30%.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #522   +/-   ##
=======================================
  Coverage   93.89%   93.90%           
=======================================
  Files          95       96    +1     
  Lines        4014     4017    +3     
=======================================
+ Hits         3769     3772    +3     
  Misses        245      245           

Files Changed	Coverage Δ
gptcache/manager/eviction/distributed_cache.py	87.50% <ø> (-2.16%)	⬇️
gptcache/manager/eviction/redis_eviction.py	91.89% <91.89%> (ø)
gptcache/manager/eviction/manager.py	100.00% <100.00%> (ø)

[a9raag]

/assign @SimFG

[SimFG]

/lgtm
/approve

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[marioplumbarius]

I still see the issue.