fix: disallow keys of JS Object prototype for safety

[wschurman]

Why

This PR addresses this comment: #233 (comment)

Essentially, we want to disallow naming entity fields the same as some predefined JS prototype fields so that code in entity that uses for .. in loops over the fields object aren't accidentally unsafe (it's too easy a mistake to make).

How

Disallow fields, add test.

Test Plan

Run test.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

@@           Coverage Diff            @@
##             main      #236   +/-   ##
========================================
  Coverage        ?   100.00%           
========================================
  Files           ?        69           
  Lines           ?      1899           
  Branches        ?       262           
========================================
  Hits            ?      1899           
  Misses          ?         0           
  Partials        ?         0           

Flag	Coverage Δ
integration	100.00% <100.00%> (?)
unittest	100.00% <100.00%> (?)

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[ide]

Important typo to fix mentioned inline.