[Contract] Standardize event name trimming

[Yunusabdul38]

Description: Ensure event names are cleanly stored by trimming leading and trailing whitespace during registration to prevent UI inconsistencies. Tasks:

Implement name sanitization in register_event.
Trim the name field before persisting to storage.
Add a test case with intentionally messy names.

[Chibey-max]

@Chibey-max has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

i would like to work on this

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Congratulations, @Chibey-max! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

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[drips-wave]

This issue has been completed by @Chibey-max as part of the Stellar Wave Program's 3rd Wave 🥳

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