Add toString() and equals() implementations for core domain types (Table, Row, Value, Column) #324

Hi,

for many relevant domain types like

• Table
• Row
• Value
• Column

there are currently no implementations of toString() and equals() (and, by implication, hashCode()). This is a significant blocker for making reliable assertions across different datasets and hinders test readability and diagnostics.

My current workaround is:

Assertions.assertThat(actualRows)
  .usingElementComparator(new CustomRowComparator())
  .withRepresentation(new CustomRowRepresentation())
  .containsExactlyInAnyOrderElementsOf(expectedRows);

I would like to contribute a fix by adding consistent equals(), hashCode(), and toString() implementations for the classes above.