Ensure Serializer runtime exceptions are rethrown as IOException

[jack-berg]

Resolves #6946, #6916.

@laurit interested in your thoughts on this as well, since its about the stateless marshalers.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.11%. Comparing base (77b1f64) to head (4960e78).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6969      +/-   ##
============================================
+ Coverage     90.09%   90.11%   +0.02%     
  Complexity     6600     6600              
============================================
  Files           730      730              
  Lines         19843    19852       +9     
  Branches       1955     1955              
============================================
+ Hits          17877    17890      +13     
+ Misses         1371     1367       -4     
  Partials        595      595              

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[laurit]

Looks good to me. I don't see too many alternatives. I guess instead of UncheckedIOException could use a sneaky throw hack and throw the IOException without declaring it, but the current solution is probably easier to understand. Another alternative would be to reimplement the forEach and introduce a ThrowingConsumer, but that isn't desirable because we'd need to use iterator in our forEach variant while IdentityHashMap etc. implement it without extra allocations.