Add parameter to scalar conversion functions specifying overflow behavior

[wolffcm]

Currently our conversion functions like int(), uint() will silently give a wrong answer if you try to convert a value that does not fit into the destination type. Here's an example:

$ flux repl
> uint(v: -1)
18446744073709551615

We should add a parameter to these functions that specify what to do if the input value does not fit. By default we can keep the current behavior. Here's a possible way to do it:

$ flux repl
> uint(v: -1, errOnOverflow: true)
Error: cannot represent value -1 as an uint

DOD: numeric conversion functions provide a way to error on overflow, and have related tests

[github-actions]

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