Fix panic on Arazzo exponents above 1000000

[SebTardif]

ValidateBytes panics on an Arazzo document that contains a decimal exponent big.Rat cannot parse.

retryAfter is a number with minimum: 0. A value such as 1e1000001 passed the normalizer because the exponent was compared only with the 16MiB byte budget. math/big.Rat.SetString accepts an exponent of 1000000 and rejects 1000001. JSON Schema then nil-dereferences while comparing that number with minimum.

The normalizer now returns the existing limit error for an absolute decimal exponent above 1000000, before schema validation. An exponent of 1000000 still validates. The byte budget check is unchanged.

TestFoundationCapsBeforeCompilation covers retryAfter: 1e1000001, retryAfter: 1e-1000001, and the accepted boundary 1e1000000.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.66%. Comparing base (a300515) to head (96b80e5).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #334   +/-   ##
=======================================
  Coverage   98.66%   98.66%           
=======================================
  Files          94       94           
  Lines       12310    12310           
=======================================
  Hits        12146    12146           
  Misses        139      139           
  Partials       25       25           

Flag	Coverage Δ
unittests	98.66% <100.00%> (ø)

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