Add helper for computing the percentage change in a creator's key price over a configurable time window

[Chucks1093]

Summary

The creator detail and trending endpoints both need a price change percentage over different windows (1h, 24h, 7d). Each currently computes this differently with duplicated time window logic. A shared helper should accept a configurable window and return the percentage change for any creator.

Scope

• Add computePriceChange(creatorId: string, windowMs: number, db: Database): Promise<number | null>
• Fetch the oldest snapshot within the window and the latest snapshot; return null if fewer than two snapshots exist
• Return the percentage change as a signed float rounded to two decimal places
• Add unit tests: positive change, negative change, null when only one snapshot, null when no snapshots

Acceptance Criteria

• Positive price change returns correct positive percentage
• Negative price change returns correct negative percentage
• Fewer than two snapshots returns null
• Percentage rounded to two decimal places
• Both creator detail and trending endpoints use the helper

ETA: 12 hours

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[jotel-dev]

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kindly assogn me

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[ZeePearl56]

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I would like to work on this issue.

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[KingDavid9999]

@KingDavid9999 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi maintainer, I'd very much appreciate the opportunity to work on this issue.
Having reviewed the acceptance criteria, I'm confident that I'd be able to have a PR up shortly after being assigned.
Kindly assign this issue to me.
Thank you!

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[Godfrey-Delight]

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Hello maintainer, please can I be assigned to this issue?

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[Caneryy]

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Hi maintainer, can I work on this issue?

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