Add u256 conversions #18758

Job	Run time
build-sway-lib-std	1m 28s
get-fuel-core-version	49s
build-sway-lib-core	1m 3s
build-reference-examples	1m 32s
build-sway-examples	3m 40s
forc-fmt-check-sway-examples	57s
forc-fmt-check-sway-lib-core	1m 8s
forc-fmt-check-sway-lib-std	1m 3s
build-forc-doc-sway-lib-std	2m 14s
build-forc-test-project	5m 42s
build-mdbook	4m 19s
forc-fmt-check-panic	1m 46s
cargo-build-workspace	3m 30s
cargo-clippy	58s
cargo-run-e2e-test-evm	2m 54s
cargo-fmt-check	15s
cargo-run-e2e-test-midenvm	2m 42s
cargo-test-lib-std	3m 3s
cargo-toml-fmt-check	14s
forc-pkg-fuels-deps-check	16s
forc-run-benchmarks	5m 57s
forc-unit-tests	3m 56s
cargo-test-sway-lsp	5m 9s
cargo-test-workspace	5m 51s
cargo-unused-deps-check	4m 8s
pre-publish-check	0s
cargo-run-e2e-test	19m 8s
cargo-run-e2e-test-release	21m 24s
cargo-test-forc-debug	4m 11s
notify-slack-on-failure	2s
publish	0s
build-publish-master-image	0s
build-publish-release-image	0s
Build and upload forc binaries to release	0s
	1h 49m 19s

Provide feedback