feat: WIP organize extensions

[zcstarr]

WIP to start organizing the code for extensions to act as a pathway to upgradeability for the open-rpc spec

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 83.78378% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 98.31%. Comparing base (280f4de) to head (4162560). Report is 1 commits behind head on master.

Files	Patch %	Lines
src/validate-open-rpc-document.ts	71.42%	6 Missing :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##            master     #853      +/-   ##
===========================================
- Coverage   100.00%   98.31%   -1.69%     
===========================================
  Files           13       14       +1     
  Lines          322      357      +35     
  Branches        74       77       +3     
===========================================
+ Hits           322      351      +29     
- Misses           0        6       +6     

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