Add equals/hashCode to MigrationResult

[evanofficial]

Summary

Implement value-based equals() and hashCode() for MigrationResult, based on success status, source/target versions, domain, and duration.

This replaces the identity-based comparison noted in the class Javadoc, making it safe to use MigrationResult in collections and assertions.

Changes

MigrationResult.java:

• Added equals() using instanceof pattern matching (matching DataVersion style)
• Added hashCode() using Objects.hash()
• Updated class Javadoc to reflect value-based equality
• Added java.util.Objects import

MigrationResultTest.java:

• Added 5 tests in new EqualsAndHashCode nested class:
  • Equal values → equals() returns true
  • Different success status → returns false
  • Different versions → returns false
  • Equal objects → consistent hashCode()
  • Null → returns false

Fixes #222

[Splatcrafter]

Thanks for your PR again! I will look over it tomorrow as soon as i'm working.