Add transaction hash validation utility

[therealjhay]

Description: The codebase has no utility for validating Stellar transaction hashes. This is needed for looking up transactions by hash.

Requirements:

• Create validateTransactionHash(hash: string): boolean
• Validate 64-character lowercase hex string
• Export alongside other utilities
• Add unit tests

Suggested execution steps:

1. Implement: /^[0-9a-f]{64}$/.test(hash)
2. Add JSDoc
3. Add tests for valid hash, invalid length, uppercase, non-hex chars

Example commit message:

feat(stellar-utils): add transaction hash validation utility

validateTransactionHash ensures a 64-character lowercase hex string
format for Stellar transaction hashes.

[kingAkinwale]

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

Hi, I'd love to work on this. Can i get this please

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

[charlesejemai-cyber]

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

hi i would like to work on this, thanks

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

[wagmiiii]

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

please assign to me

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

[Caneryy]

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

Hi maintainer, can I work on this issue?

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

[drips-wave]

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

🧑‍💻 @kingAkinwale: 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.

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