chore: u64 might require special treatment

[gastonfournier]

About the changes

Using u64 will require us to use bigint on the server side. It may also bring other interoperability problems with other languages. u32 should be enough and compatible with most languages.

As specified in https://www.rfc-editor.org/rfc/rfc7159:

This specification allows implementations to set limits on the range
and precision of numbers accepted. Since software that implements
IEEE 754-2008 binary64 (double precision) numbers [IEEE754] is
generally available and widely used, good interoperability can be
achieved by implementations that expect no more precision or range
than these provide, in the sense that implementations will
approximate JSON numbers within the expected precision. A JSON
number such as 1E400 or 3.141592653589793238462643383279 may indicate
potential interoperability problems, since it suggests that the
software that created it expects receiving software to have greater
capabilities for numeric magnitude and precision than is widely
available.

Note that when such software is used, numbers that are integers and
are in the range [-(253)+1, (253)-1] are interoperable in the
sense that implementations will agree exactly on their numeric
values.

[sighphyre]

Yeah, sounds good to me