feat: impl Default for U128

[asterite]

Description

Problem

Resolves #6982

Summary

Additional Context

Documentation

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[github-actions]

Execution Report

Program	Execution Time	%
sha256_regression	0.100s	0%
regression_4709	0.001s	0%
ram_blowup_regression	0.580s	0%
rollup-root	0.105s	-1%
rollup-block-merge	0.105s	-1%
rollup-base-public	1.430s	0%
rollup-base-private	0.619s	-2%
private-kernel-tail	0.022s	0%
private-kernel-reset	0.390s	0%
private-kernel-inner	0.120s	1%

[github-actions]

Compilation Report

Program	Compilation Time	%
sha256_regression	1.368s	-2%
regression_4709	0.774s	-2%
ram_blowup_regression	15.580s	-2%
rollup-root	3.680s	-22%
rollup-block-merge	4.630s	24%
rollup-base-public	29.800s	-7%
rollup-base-private	12.200s	-6%
private-kernel-tail	0.971s	-1%
private-kernel-reset	6.986s	-3%
private-kernel-inner	2.398s	3%

[github-actions]

Execution Memory Report

Program	Peak Memory
keccak256	74.65M
workspace	123.87M
regression_4709	315.98M
ram_blowup_regression	512.48M
rollup-base-public	773.37M
rollup-base-private	352.03M
private-kernel-tail	181.12M
private-kernel-reset	255.43M
private-kernel-inner	215.04M

[github-actions]

Compilation Memory Report

Program	Peak Memory
keccak256	78.55M
workspace	123.86M
regression_4709	422.96M
ram_blowup_regression	1.58G
rollup-base-public	2.52G
rollup-base-private	1.24G
private-kernel-tail	200.40M
private-kernel-reset	716.42M
private-kernel-inner	292.10M