fix: preserve repeated blob matches in getBlobs

[solanaXpeter]

Motivation

getBlobs currently collapses repeated versioned hash matches to the first index, which drops valid blob occurrences when a block repeats the same commitment.

Description

• preserve every blob index that matches a requested versioned hash
• keep results grouped by request order while preserving block order within each hash group
• add focused coverage for repeated-hash selection

No linked issue.

AI Assistance Disclosure

• External Contributors: I have read the contributor guidelines and disclosed my usage of AI below.
• AI assistance used for implementation drafting and local validation.

[gemini-code-assist]

Code Review

This pull request refactors the logic for retrieving blob indices by versioned hashes into a reusable utility function, getBlobIndicesByVersionedHashes. It replaces inline implementations in the beacon blocks API with this new function and adds corresponding unit tests. I have no feedback to provide.