YAML vs 64-bit

[arnetheduck]

As noted here: ethereum/consensus-specs#224 (comment), keeping serialized tests in YAML format might be problematic for some "standard" yaml parsers, for 64-bit numbers.

Here's a few options to fix this:

• use strings instead of numbers (adds another decoding step)
• use a custom YAML parser in affected languages (maybe reasonable, these implementations will need to deal with this problem regardless - looking at you, Javascript/Typescript)
• use SSZ throughout (not good for some of the testing design goals, like comment support)

refs:

• https://stackoverflow.com/questions/209869/what-is-the-accepted-way-to-send-64-bit-values-over-json
• sample issue in popular app: 64bit integers are not properly handled elastic/kibana#1274
• https://yaml.org/spec/1.2/spec.html - In some languages (such as C), an integer may overflow the native type’s storage capability. A YAML processor may reject such a value as an error, truncate it with a warning, or find some other manner to round-trip it. In general, integers representable using 32 binary digits should safely round-trip through most systems.