Add missing tests for number parsing

[CXWorks]

Hi,

Thanks for your time & patience to review this PR.

We are researchers focusing on Rust unit tests, we revised our tool for better readability. By examine the existing code, we found several unit tests can be added to improve the repo's overall unit test coverage(this project is already been well tested).

Thanks again for your time.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #1769 will improve performances by 13.57%

_{Comparing CXWorks:main (4a107b8) with main (fcc9f16)}

Summary

⚡ 1 improvements
✅ 23 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	CXWorks:main	Change
⚡	number	244.2 ns	215 ns	+13.57%

[Geal]

Thank you! New tests always help!