Added a config to limit the code-gen and class loading

[volauvent]

The config sets the maximum number of fast SerDes classes generated and loaded. It helps to limit the metaspace and codecache usage brought by fast-avro runtime code-gen and class loading.

The limit config can be set via FastSerdeCache constructors.

[codecov-commenter]

Codecov Report

Merging #83 into master will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #83   +/-   ##
=========================================
  Coverage     53.42%   53.42%           
  Complexity      275      275           
=========================================
  Files            39       39           
  Lines          1662     1662           
  Branches        206      206           
=========================================
  Hits            888      888           
  Misses          692      692           
  Partials         82       82           

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