[bercedev]

Closes #16

• QuickbaseQueryBuilder gets Skip(int count) and Top(int count), each returning the builder and each with an XML doc comment. They store an int?.
• Build() sets Options only when one of them was called, with the other left at 0. Otherwise Options stays null, as today.
• In Options, skip and top now use DefaultValueHandling = DefaultValueHandling.Ignore, so Skip(100) alone serializes "skip":100 with no "top" key. compareWithAppLocalTime is unchanged. QueryAllRecords is left out, as the issue says.

Tests: new QuickbaseNet.UnitTests/Tests/QuickbaseQueryBuilderTests.cs, one test per point in the issue:

• .Skip(100).Top(50) gives Options.Skip 100 and Options.Top 50;
• a request built without either has Options == null;
• JsonConvert.SerializeObject of a .Skip(100) request contains "skip":100 and no "top".

dotnet test: 11 passed. dotnet build QuickbaseNet gives 0 warnings and 0 errors across its targets. I ran both with the .NET 8 SDK, offline in a container.