Rust 1.77 toolchain - Fix alignment and layout for z_owned_reply_t

[Mallets]

Rust 1.77 has been released: https://releases.rs/docs/1.77.0/
Along with 1.77 it comes the following change: rust-lang/rust#116672

This means that u128 have now a different alignment on x86 targets, making the compilation of zenoh-c to fail on x86 when compiled with Rust 1.77.

This patch fixes the memory layout and alignment of the z_owned_reply_t affected by that change.

However, I suggest to not merge this PR straight away since there are projects that depend on main branch of zenoh-c and they will not use Rust 1.77. E.g.: https://github.com/ros2/rmw_zenoh will use the Rust shipped version in Ubuntu 24.04, which is 1.75.

An option could be to have different layout depending on the compiler version but this capability seems to be still unstable: https://doc.rust-lang.org/unstable-book/language-features/cfg-version.html
A larger change may be hence needed in Zenoh, particularly in the ZenohId type to avoid using u128 at all.

[eclipse-zenoh-bot]

@Mallets If this pull request contains a bugfix or a new feature, then please consider using Closes #ISSUE-NUMBER syntax to link it to an issue.

[Mallets]

Superseded by #298