Address Rust Package build

[mjp41]

Addresses #828

Also, finally tidying, so we can release an updated Rust package and bump the snmalloc version number in one go.

[mjp41]

@SchrodingerZhu I have also put some draft release notes on the release page. Could you take a look at those as well. Thanks

[SchrodingerZhu]

LGTM!

[Copilot]

Pull request overview

This PR addresses issue #828 by adding a repository-level Cargo workspace so snmalloc-rs can be consumed via a git dependency pointing at the repo root, while also aligning the Rust crate documentation/versioning for a 0.7.4 release.

Changes:

• Add a top-level Cargo.toml workspace that includes snmalloc-rs, snmalloc-sys, and xtask.
• Remove the sub-workspace definition from snmalloc-rs/Cargo.toml now that the workspace is defined at the repo root.
• Update Rust crate docs/changelog to reflect version 0.7.4.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
snmalloc-rs/README.md	Updates the dependency snippet to snmalloc-rs = "0.7.4".
snmalloc-rs/Cargo.toml	Removes the local [workspace] section, leaving this as a package manifest within the new root workspace.
snmalloc-rs/CHANGELOG.md	Adds a 0.7.4 entry describing upstream tracking and repository move context.
Cargo.toml	Introduces a repository-level Rust workspace with resolver v2 and the Rust crates as members.

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[mjp41]

@SchrodingerZhu, If I release this branch with a tag 0.7.4 can you create the package on crates?

[SchrodingerZhu]

sure!