Backport to branch(3) : Refactor AssetProofComposer

[feeblefakie]

This is an automated backport of the following:

• Original PR: Refactor AssetProofComposer #333
• Backported commit: 4b93a4a

Please merge this PR after all checks have passed.

[gemini-code-assist]

Summary of Changes

Hello @feeblefakie, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on enhancing the modularity and maintainability of the Ledger component. It involves a significant refactoring of the AssetProofComposer to decouple it from specific database implementations and a strategic relocation to a more appropriate package. Furthermore, it streamlines test code by centralizing frequently used cryptographic constants, thereby reducing redundancy and improving test clarity.

Highlights

• AssetProofComposer Refactoring: The AssetProofComposer class has been refactored to remove its direct dependency on ScalarDB's Put object, making it more generic and reusable. A new create method was introduced that accepts primitive data types, and the logic for extracting these from Put objects was moved to ScalarTamperEvidentAssetLedger.
• Package Relocation: The AssetProofComposer class has been moved from the com.scalar.dl.ledger.database.scalardb package to the more general com.scalar.dl.ledger.database package, reflecting its reduced dependency on ScalarDB specifics.
• Centralized Test Constants: Common test constants, specifically private keys and certificates, have been extracted from various test and integration-test files into a new dedicated TestConstants.java file. This improves code organization, reduces duplication, and simplifies maintenance across test suites.

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[gemini-code-assist]

Code Review

This pull request is a backport of a refactoring that primarily focuses on two areas. First, it decouples AssetProofComposer from ScalarDB-specific dependencies by moving the logic that handles com.scalar.db.api.Put objects into ScalarTamperEvidentAssetLedger. This is a good design improvement that increases modularity. Second, it centralizes duplicated test constants for private keys and certificates into a new TestConstants class, which improves maintainability by reducing code duplication. The changes are well-executed and improve the overall code quality. I have reviewed the changes and found no issues.