bitcoind: fix byte order of block hash from getrawblockbyheight

[Andezion]

Fixes #9465

Summary

getrawblockbyheight_callback() parsed the plugin s blockhash field with json_to_sha256(), which hex-decodes without reversing bytes. Every other block hash / txid parser in the codebase (like bitcoin_blkid_from_hex, bitcoin_txid_from_hex, json_to_bitcoin_blkid) reverses the bytes after decoding, since bitcoind displays hashes in rpc/json in the opposite byte order to the internal representation used for hashing and db storage

Most callers of bitcoind_getrawblockbyheight() ignore the parsed blkid and recompute it from the block header instead, so they were unaffected. But process_getfilteredblock_step1() (used for on-demand gossip block backfill) trusts the parsed value directly, and wallet_filteredblock_add() writes it straight into blocks.hash - producing rows with inconsistent endianness relative to rows written by normal chain-tip sync

Fix

Parse blockhash with json_to_bitcoin_blkid() instead, matching every other blkid parser in the codebase

Changelog-None

Important

26.09 FREEZE August 5th: Non-bugfix PRs not ready by this date will wait for 26.12.

RC1 is scheduled on August 17th

The final release is scheduled for September 7th.

Checklist

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• The changelog has been updated in the relevant commit(s) according to the guidelines.
• Tests have been added or modified to reflect the changes.
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