Fix equals() symmetry issue in ModifiableLengthField

[ic0ns]

Summary

• Fixed SpotBugs issue EQ_OVERRIDING_EQUALS_NOT_SYMMETRIC in ModifiableLengthField
• Ensured equals() method maintains symmetry with ModifiableInteger and its subclasses
• Added comprehensive test coverage for the symmetry fix

Changes

• Modified ModifiableLengthField.equals() to handle comparison with different types correctly:
  • When comparing with another ModifiableLengthField: checks both value and reference equality
  • When comparing with other ModifiableInteger subclasses: only checks value equality for symmetry
• Added ModifiableLengthFieldSymmetryTest with tests for:
  • Symmetry between ModifiableLengthField and ModifiableInteger
  • Handling of null values
  • Reference equality between ModifiableLengthField instances
  • Transitivity of equals
  • Edge cases and inheritance hierarchy

Test plan

• Run existing ModifiableLengthFieldTest tests - all pass
• Run new ModifiableLengthFieldSymmetryTest tests - all pass
• Verify code compiles and passes spotless formatting
• Confirm the fix resolves the SpotBugs warning

This fix ensures that if a.equals(b) returns true, then b.equals(a) also returns true, which is required by the equals() contract in Java.