fix(api): end telemetry spans when middleware throws

[wangjingshuiku]

Checklist

• My change requires a documentation update, and I have done it. (Not applicable: no public API or configuration changes.)
• I have added tests to cover my changes. (No new test was added; the API package type-check passes.)
• I have filled out the description and linked the related issues. (No related issue.)

Description

End the active middleware span from a finally block so it is closed on both successful requests and exceptions from downstream middleware. Return values and error propagation remain unchanged.

Motivation and Context (Optional)

The previous implementation called span.end() only after next() resolved. If next() threw, the function exited before ending the span, leaving incomplete telemetry.

Validation: pnpm --filter @blobscan/api type-check

Related Issue (Optional)

None.

Screenshots (if appropriate):

Not applicable.

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Latest commit: 0507cd0

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