bump version to 0.7.2

[SchrodingerZhu]

No description provided.

[Copilot]

Pull Request Overview

This PR bumps the snmalloc-rs library version from 0.3.8 to 0.3.9 to track upstream snmalloc version 0.7.2.

• Updates package versions in both main and sys crate Cargo.toml files
• Updates git submodule reference to point to newer snmalloc commit
• Adds changelog entry documenting the version bump

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
snmalloc-sys/snmalloc	Updates git submodule commit hash to track upstream
snmalloc-sys/Cargo.toml	Bumps snmalloc-sys version from 0.3.8 to 0.3.9
Cargo.toml	Bumps main package version and dependency version to 0.3.9
CHANGELOG.md	Adds entry for version 0.3.9 referencing upstream 0.7.2

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[Copilot]

The changelog entry mentions tracking upstream version 0.7.2, but the PR title says 'bump version to 0.7.2' while the actual version being bumped to is 0.3.9. This inconsistency could confuse users about which version they're actually getting.

Suggested change

	- Tracking upstream to match version 0.7.2
	- Package version 0.3.9 now tracks upstream version 0.7.2

[SchrodingerZhu]

@mjp41 could you take a look at the windows failure?