feat(demo/ufmt): add some usefull missing methods: (Fprintx, AppendX, SprintX, PrintX)

[gfanton]

This PR enhances the ufmt package by adding missing methods such as FprintX, AppendX, SprintX, and PrintX. These additions address the package's previous limitations. It also centralizes and improves the logic in a printer, similar to the approach used by the fmt package.

Additionally, I have added new tests and moved the logic of Println test into Sprint test (since the logic has been moved into the printer, we can now test it using the Sprint function)

Note: I added these functions mainly because I enjoy using fmt.FprintX with strings.Builder and bytes.Buffer.

[Gno2D2]

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[moul]

It looks good; however, this PR makes me feel that we really need a way to generate a "gas-report.txt" file when running gno test or gno benchmark. This would allow us to measure the impact of those changes.
Can we prioritize the gas-report system if not yet developed, possibly with a bounty? Else, we should start using it.

cc @petar-dambovaliev @mvertes @thehowl