Issue when calling repeat() after using index()

[Misha1Shevchuk]

To reuse common field values we often use EntityBuilder, for example

`@IsTest
private class AtkBugTest {

@IsTest
private static void test1() {
    ATK.SaveResult atkResult = ATK.prepare(Opportunity.SObjectType, 10)
        .build(new OpportunityEntityBuilder())
        .field(Opportunity.Name).repeat('Test Name')
        .mock();

    List<Opportunity> opportunities = (List<Opportunity>) atkResult.get(Opportunity.SObjectType);
    for (Opportunity opp : opportunities) {
        Assert.areEqual('Test Name', opp.Name); // this fails, actual result is OPPORTUNITY-NAME-1
    }
}

public class OpportunityEntityBuilder implements ATK.EntityBuilder {

    public void build(ATK.Entity entity, Integer size) {
        entity
            .field(Opportunity.Name).index('OPPORTUNITY-NAME-{0}')
            .field(Opportunity.Description).repeat('Test Description')
            .field(Opportunity.CloseDate).repeat(Date.today().addMonths(1));
    }
}

}`