use noOp cache instead of null when instantiating typedSparkeySideInput

[pgoggijr]

When attempting to access an element in a side input instantiated by typedSparkeySideInput where cache isn't specified, the following error is thrown since the cache is explicitly set to null:

Error message from worker: java.lang.NullPointerException: Cannot invoke "com.spotify.scio.util.Cache.get(Object, scala.Function0)" because the return value of "com.spotify.scio.extra.sparkey.instances.TypedSparkeyReader.cache()" is null
	com.spotify.scio.extra.sparkey.instances.TypedSparkeyReader.get(TypedSparkeyReader.scala:42)
	com.spotify.scio.extra.sparkey.instances.TypedSparkeyReader.get(TypedSparkeyReader.scala:31)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 61.30%. Comparing base (2fe2258) to head (62a901b).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...scala/com/spotify/scio/extra/sparkey/package.scala	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5469      +/-   ##
==========================================
- Coverage   61.31%   61.30%   -0.01%     
==========================================
  Files         312      312              
  Lines       11068    11070       +2     
  Branches      792      773      -19     
==========================================
+ Hits         6786     6787       +1     
- Misses       4282     4283       +1     

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