fix: don't U128::from_integer(u128)

[asterite]

In Noir we are removing the (private) built-ins as_field and from_field, which allowed casting any type to and from Field by truncating its bits. This uncovered two bugs where we were doing U128::from_integer(x) with x itself being a U128. That code won't compile anymore (and I think it was incorrect) so I'm doing those changes in this PR.

See noir-lang/noir#6845

[github-actions]

Changes to public function bytecode sizes

Generated at commit: 80510e6ab96564eb54e7dea96e3dfef7835a69df, compared to commit: e867e87e4e5e4b140bf8ec3e5ee75abd24571bb1

🧾 Summary (100% most significant diffs)

Program	Bytecode size in bytes (+/-)	%
Lending::public_dispatch	-47 ✅	-0.17%
Lending::get_position	-66 ✅	-1.40%

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Full diff report 👇

Program	Bytecode size in bytes (+/-)	%
Lending::public_dispatch	27,782 (-47)	-0.17%
Lending::get_position	4,662 (-66)	-1.40%