build!: require rustc 1.85 and Rust 2024 edition

[esteve]

This PR updates the requirement for the rustc compiler to 1.85 and the minimum supported edition of Rust to 2024.

[luca-della-vedova]

Somewhat tangential to the 1.85 or no 1.85 decision, but this PR and its almost 4000 diff mostly due to format changes will really wreak havoc of merge conflicts in all the PRs that are currently open.

In an ideal world we would get through some of the review backlog and review / merge open PRs first.
Iin a less ideal world we would configure rustfmt to use the previous rust edition and undo format changes here.
In an even less ideal world we would merge this and commit to solve merge conflicts for all open PRs to make contributor's life easier.
In the worst world I can imagine this gets merged as is and now all contributors with long open PRs need to navigate large scale merge conflicts.

[esteve]

@luca-della-vedova yeah, I agree, it's not an ideal situation. I've kept the formatting changes in a separate commit so they can be easily reverted/removed. I'd rather keep the 1.85 requirement given that requiring 1.75 is not providing any benefit and in fact, it's causing issues with some of the dependencies. We could postpone the switch to the 2024 edition, though still keep the code changes (i.e. unsafe blocks).

For the next release of rclrs I want to include at least, your PR with the dynamic publishers/subscribers, the switch to 1.85 and some of the smaller PRs (warnings, QoS, etc). After all those PRs are merged, it'd be a good moment to switch to Rust 2024 and reformat the source code.

However, formatting changes seem to be mostly related to the ordering of the imports, and not much else.