Fix typo: multiplaction -> multiplication in DEVELOPING.md

[zent7x]

Summary

• Fixed typo in DEVELOPING.md: "Two multiplaction operators" -> "Two multiplication operators"

Test plan

• Verified the fix is a simple typo correction with no functional changes

[DaiFoundation-DevOps]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}