Tidy-up in json test module (#8431)
Tidy-up in json test module (#8431)

* Switch json testing 'roundTrip()' to use FixedBufferStream, improve error handling, remove comptime from param

* Add 'try' to calls to roundTrip() that can now return an error

* Remove comptime from params in json testing, replace expect(false) with letting error propagate

* Add 'try' to calls to ok() that can now return an error

Co-authored-by: Lewis Gaul <8e32f2aab1da15dda32e124730791ad26c65b6a9@cisco.com>
zig-lang/zig,andrewrk/zig,andrewrk/zig,zig-lang/zig,zig-lang/zig