feat: Add migration utility for book state management models

[devin-ai-integration]

feat: Add migration utility for book state management models

Summary

This PR introduces a BookMigrationUtility class that enables conversion from the old book model (separate classes: AvailableBook, BookOnHold, CheckedOutBook) to the new State pattern implementation (Book class with BookState interface). The utility preserves all book properties including ID, type, version numbers, patron information, branch details, and timestamps during migration.

Key changes:

• Added BookMigrationUtility.java with three overloaded migrate() methods for each old model type
• Uses reflection to set the internal state since Book constructor defaults to AvailableState
• Created comprehensive unit tests covering all migration scenarios including edge cases
• Maintains version numbers for optimistic locking and preserves all business-critical data

Review & Testing Checklist for Human

⚠️ CRITICAL - This code has not been runtime tested due to environment issues

• Run the migration tests locally - Verify BookMigrationUtilityTest passes and migration actually works end-to-end
• Test data preservation - Confirm all fields (bookId, bookType, version, patron, branch, timestamps) are correctly preserved during migration
• Verify state behavior - Test that migrated books behave correctly with state transitions (checkout, hold, return operations)
• Check reflection compatibility - Ensure the reflection approach works in your deployment environment (security policies, module system)
• Test edge cases - Try restricted books, different version numbers, and error scenarios to ensure robustness

Recommended test plan: Create sample instances of each old model type, migrate them, and verify both data preservation and that business operations (place hold, checkout, return) work correctly on the migrated objects.

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    subgraph "Old Model Package"
        AvailableBook["model/AvailableBook.java"]:::context
        BookOnHold["model/BookOnHold.java"]:::context  
        CheckedOutBook["model/CheckedOutBook.java"]:::context
    end
    
    subgraph "New Model Package"
        Book["new_model/Book.java"]:::context
        BookState["new_model/BookState.java"]:::context
        AvailableState["new_model/AvailableState.java"]:::context
        OnHoldState["new_model/OnHoldState.java"]:::context
        CheckedOutState["new_model/CheckedOutState.java"]:::context
        MigrationUtility["new_model/BookMigrationUtility.java"]:::major-edit
    end
    
    subgraph "Tests"
        MigrationTest["test/.../BookMigrationUtilityTest.groovy"]:::major-edit
    end
    
    subgraph "Documentation"
        README["README.md"]:::minor-edit
    end
    
    AvailableBook -->|"migrate()"| MigrationUtility
    BookOnHold -->|"migrate()"| MigrationUtility  
    CheckedOutBook -->|"migrate()"| MigrationUtility
    MigrationUtility -->|"creates"| Book
    MigrationUtility -.->|"uses reflection"| Book
    Book -->|"contains"| BookState
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit
        L3[Context/No Edit]:::context
    end
    
    
    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB    
    classDef context fill:#FFFFFF

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Notes

• Environment Issue: Maven test compilation failed due to Java module system restrictions, preventing runtime verification of the migration utility
• Reflection Usage: The utility uses reflection to set the internal state field of Book objects since the constructor always creates AvailableState initially
• Data Mapping: Carefully mapped all fields from old models to preserve business-critical information like patron IDs, hold timestamps, and version numbers
• Session Info: Requested by @callummiles - Link to Devin run: https://app.devin.ai/sessions/9f4f15a000fe4d5c82b41505b06c8c77

⚠️ Important: This code compiles successfully but has not been runtime tested. Please run the tests locally before merging to ensure the migration utility works correctly in practice.

[devin-ai-integration]

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[callummiles]

Make sure you don't forget to also update the ReadME with your changes