debug trace alignment: storage encoding

[macfarla]

• memory words and storage keys/values are 0x prefixed and left-padded to 32 bytes per the execution-apis opcode tracer spec.
• error type is String rather than String[] with a single element
  Refs debug RPC endpoints standardization #10115 - addresses 2,4

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• Considered the changelog and included an update if required.

Locally, you can run these tests to catch failures early:

• spotless: ./gradlew spotlessApply
• unit tests: ./gradlew build
• acceptance tests: ./gradlew acceptanceTest
• integration tests: ./gradlew integrationTest
• reference tests: ./gradlew ethereum:referenceTests:referenceTests
• hive tests: Engine or other RPCs modified?

[Copilot]

Pull request overview

Updates debug trace output formatting to match the execution-apis opcode tracer spec (32-byte, 0x-prefixed storage keys/values) and adjusts the error field to serialize as a single string.

Changes:

• Normalize storage keys/values in struct logs and trace JSON fixtures to 0x-prefixed, left-padded 32-byte hex.
• Add a helper (toBytes32Hex) used for storage formatting.
• Change StructLogWithError.error from String[] to nullable String in JSON output.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/internal/results/StructLog.java	Formats storage entries as bytes32 hex via new helper.
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/internal/results/StructLogWithError.java	Changes JSON error field type from array to string and omits when null.
ethereum/api/src/test/java/org/hyperledger/besu/ethereum/api/jsonrpc/internal/results/StructLogTest.java	Updates expectations for new storage encoding.
ethereum/api/src/test/resources/.../debug_traceBlock_default.json	Updates expected trace storage encoding to bytes32 hex.
ethereum/api/src/test/resources/.../debug_traceBlock_disableMemory.json	Updates expected trace storage encoding to bytes32 hex.
ethereum/api/src/test/resources/.../debug_traceBlock_disableStack.json	Updates expected trace storage encoding to bytes32 hex.

[usmansaleem]

LGTM