Llmcache example

[Spartee]

LLMCache notebook example in docs.

Other changes

• additions to the test suite for testing the index

[codecov-commenter]

Codecov Report

Merging #21 (1250d1d) into main (71b0bb8) will increase coverage by 5.44%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##             main      #21      +/-   ##
==========================================
+ Coverage   81.31%   86.76%   +5.44%     
==========================================
  Files          12       11       -1     
  Lines         455      461       +6     
==========================================
+ Hits          370      400      +30     
+ Misses         85       61      -24     

Impacted Files	Coverage Δ
redisvl/index.py	90.43% <60.00%> (+8.19%)	⬆️
redisvl/llmcache/semantic.py	93.84% <81.81%> (+5.51%)	⬆️
redisvl/llmcache/base.py	90.90% <100.00%> (+38.27%)	⬆️

... and 3 files with indirect coverage changes