fix(xcm): use single encoding for XCM messages

[peterwht]

Summary

Closes #_

• [y] y/n | Does it introduce breaking changes? -> kinda, see notes below.
• [y] y/n | Is it dependant on the specific version of cargo-contract or pallet-contracts?

A later release of pallet-contracts changes the expected XCM message format for xcm_execute and xcm_send from requiring a double encoded message to a single encoded message.

Compatible with pallet-contracts on polkadot-v1.11.0 and greater.

Description

ink!'s XCM support was originally merged on polkadot-v1.10.0, where XCM used execute_blob and send_blob. These accepted an encoded XCM message, which required that ink! double encode XCM messages.

However, in this commit Revert execute_blob and send_blob (#4266) , execute_blob was replaced by execute which accepts a VersionedXcm<RuntimeCall> message. This requires that ink! single encodes the XCM message.

XCM support in ink! has not had an official release, and remained in the master branch only. Additionally, since the initial support, pallet-contracts has stabilized the XCM host fns.

Checklist before requesting a review

• My code follows the style guidelines of this project
• I have added an entry to CHANGELOG.md
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works ->
• Any dependent changes have been merged and published in downstream modules

[pgherveou]

Make sense I think if the tests are passing with a runtime that has the changed mentioned here, then it should be good to merge

[AlexD10S]

The CI failing here https://github.com/use-ink/ink/actions/runs/10586570908/job/29335623282?pr=2278 I think is the same problem we have building the docker image in cargo-contract: https://github.com/use-ink/cargo-contract/actions/runs/10556354226/job/29241730113

The nightly Rust version nightly-2024-02-08 is currently hardcoded for linting in the rust-toolchain.toml file. Does it needs to be updated?