Improve fatal error message for block read failures in BaseIndex::ProcessBlock #33659

When a block read operation fails in BaseIndex::ProcessBlock, the current error message only reports: Failed to read block %s from disk

This message doesn't provide enough context to help developers or node operators diagnose the problem.

What changed? The fatal error message now includes: The block hash (already existed) The block height A clearer description of the issue A hint to check whether the block exists in the database

Before:

FatalErrorf("Failed to read block %s from disk",
             pindex->GetBlockHash().ToString());

After

FatalErrorf("Block reading error: Could not read block with hash %s from disk at height %d. Please check if the block exists in the database and is accessible.",
             pindex->GetBlockHash().ToString(), pindex->nHeight);

Benefit: More informative error messages help node operators debug issues faster.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33659.

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NACK, feels like busywork, don't see how this improves things.