Add as_u256 for U128 #23413

Job	Run time
build-sway-lib-core	53s
build-sway-examples	1m 5s
build-sway-lib-std	50s
build-reference-examples	1m 0s
forc-fmt-check-sway-examples	36s
forc-fmt-check-sway-lib-core	53s
forc-fmt-check-sway-lib-std	41s
get-fuel-core-version	29s
build-forc-doc-sway-lib-std	1m 30s
build-forc-test-project	3m 47s
build-mdbook	7m 31s
cargo-build-workspace	2m 8s
cargo-clippy	47s
cargo-fmt-check	12s
cargo-run-e2e-test-evm	4m 13s
cargo-test-lib-std	7m 29s
check-sdk-harness-test-suite-compatibility	28s
cargo-toml-fmt-check	18s
forc-fmt-check-panic	1m 53s
forc-run-benchmarks	2m 22s
forc-unit-tests	6m 25s
cargo-test-forc	1m 31s
cargo-test-sway-lsp	7m 59s
cargo-test-workspace	4m 57s
cargo-unused-deps-check	5m 11s
forc-pkg-fuels-deps-check	12s
pre-publish-check	0s
cargo-run-e2e-test-release	11m 5s
cargo-test-forc-client	2m 51s
cargo-test-forc-debug	1m 53s
cargo-run-e2e-test	13m 43s
cargo-test-forc-node	1m 7s
notify-slack-on-failure	1s
publish	0s
build-publish-master-image	0s
build-publish-release-image	0s
Build and upload forc binaries to release	0s
verifications-complete	0s
	1h 36m 0s

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