Add `assert_approx_eq!` macro with configurable tolerance

[adams813]

Description

This issue is to track the work for: Add assert_approx_eq! macro with configurable tolerance.

Guidelines for Contributors

1. Please review the repository's CONTRIBUTING.md.
2. Fork the repository and create a new feature branch.
3. Ensure that tests are added for any new functionality.
4. Run cargo test and cargo clippy locally before submitting a PR.
5. Reference this issue in your PR description.

[Johnjnr1]

@Johnjnr1 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, I'd like to work on this issue! because I am very conversant with solving problems like this!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Johnjnr1 to this issue.

[Mkalbani]

@Mkalbani has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi maintainers. I'm a Web3 Fullstack dev. I've worked on a similar work. Would be done before the ETA. Thank you.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Mkalbani to this issue.

[wheval]

@wheval has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello i would love to work on this.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @wheval to this issue.

[drips-wave]

Congratulations, @wheval! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @wheval: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊