chore(cursor): Add Rust formatting check to Cursor rules

[HazAT]

Summary

• Added cargo fmt --all -- --check command to the Cursor rules file
• Ensures consistent Rust code formatting before committing changes
• Helps maintain code quality standards across the project

Test plan

• Updated .cursor/rules/sentry-cli-project.mdc with formatting requirement
• Verified the formatting command syntax is correct

🤖 Generated with Claude Code

[szokeasaurusrex]

We already run cargo fmt --all -- --check to verify correct formatting in CI, so there is no need for the LLM to verify it before committing.

However, running cargo fmt --all, which actually fixes formatting rather than just validating it, could in fact be useful:

Suggested change

	- Always run `cargo fmt --all -- --check` before committing to ensure consistent Rust code formatting
	- Always run `cargo fmt --all` before committing to ensure consistent Rust code formatting

I would also suggest placing this line in .cursor/rules/rust-development.mdc, as it is only relevant to Rust development.

[szokeasaurusrex]

Closing in favor of #2721