chore(pool): derive Clone and Debug on DataKey enum (#589)

[ZacLou]

Closes #589

What

Adds #[derive(Clone, Debug)] to the pool contract DataKey enum, matching the existing derives on PoolStats and LPPosition in the same file.

Notes

• The escrow contract received the same fix under [Low] refactor(escrow): derive Clone and Debug on escrow DataKey #242; this applies the identical change to the pool contract.
• No discriminants were changed, no variants were reordered.
• cargo check -p pool should pass.

[mergekeeper]

MergeKeeper review

Scope: in scope for linked issue #589.
Verdict: clean

The pull request correctly adds #[derive(Clone, Debug)] to the pool contract's DataKey enum as specified in issue #589.

Reviewed commit: 82f582bf7e24e95aa1c0616b9037707cd1dc19d1.
CI and merge eligibility are checked separately.

[mergekeeper]

Approved

The pull request correctly adds #[derive(Clone, Debug)] to the pool contract's DataKey enum as specified in issue #589.

[mergekeeper]

Merged

Merged with squash.