chore: refactor cachers to use an abstract class and interface

[quinlanj]

Why

Interfaces and abstract classes for generic cachers and secondary entity caches. Followup from https://github.com/expo/universe/pull/9106#pullrequestreview-879787342

The plan is to have:

• GenericRedisCacher (from the entity package) and GenericLocalMemoryCacher implement GenericCacher?
• SecondaryRedisEntityCache (from the entity package) and LocalMemoryAndRedisSecondaryEntityCache extending GenericSecondaryEntityCache?

Test Plan

• current tests pass

[codecov]

Codecov Report

Merging #157 (40194f3) into master (0adcf72) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #157      +/-   ##
==========================================
- Coverage   95.92%   95.85%   -0.08%     
==========================================
  Files          74       74              
  Lines        1866     1833      -33     
  Branches      204      201       -3     
==========================================
- Hits         1790     1757      -33     
  Misses         75       75              
  Partials        1        1              

Flag	Coverage Δ
integration	95.85% <100.00%> (-0.08%)	⬇️
unittest	95.85% <100.00%> (-0.08%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...tity-cache-adapter-redis/src/GenericRedisCacher.ts	100.00% <100.00%> (ø)
...ndary-cache-redis/src/RedisSecondaryEntityCache.ts	100.00% <100.00%> (ø)

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[wschurman]

(codecov looks fine btw)