Duration and timestamp types exceed range from language definition

[apasel422]

In the process of addressing the TODOs for handling timestamp/duration overflow, I noticed that this crate permits values that exceed that of the language definition

• Duration values are limited to a single int64 value, or roughly +-290 years.
• Timestamp values are limited to the range of values which can be serialized as a string: ["0001-01-01T00:00:00Z", "9999-12-31T23:59:59.999999999Z"].

In particular, the expression

timestamp('9999-12-31T23:59:59Z') + duration('1s')

evaluates to +10000-01-01T00:00:00+00:00 instead of causing an error, like the corresponding specification test.

I haven't checked other overflow cases yet, but I assume they also exist.

We should reconsider whether to directly expose chrono's types here, or whether it would be better to add wrappers, which might also be beneficial in case we ever wanted to migrate to another dependency. We could still, of course, provide conversions to and from chrono's types with the appropriate range checking.

[apasel422]

Actually I see now that there exist wrapper types already in the ser module. We should just use those in Value.

[clarkmcc]

Operation overflows were resolved in 9342b7d. I still need to investigate your second suggestion about using the wrapper types in Value rather than the chrono types directly.