A YearMonthRange column can't load an exclusive infinity) #258

Problem

Two small findings from the final pre-release analysis on add665c (pass A):

1. The non-generic CompareTo's error message breaks on a nested generic type. RangeOrder.cs:58 strips the arity from Type.Name via its backtick, but the name of a nested type inside a generic, such as List<int>.Enumerator, has none. So ((IComparable)range).CompareTo(new List<int>().GetEnumerator()) throws ArgumentOutOfRangeException: length ('-1')… instead of the intended ArgumentException naming both types. It still derives from ArgumentException, so the contract holds, but the message is garbage. Guard on IndexOf being -1.
2. A YearMonthRange column holding an exclusive infinity) can't be loaded. daterange '[2026-01-01,infinity)' in a YearMonthRange column throws InvalidOperationException ("9999-12-30 is not the last day of a month"). This is older than 10.0.0 and fails loudly. R42 deliberately uses infinity], and the docs/efcore.md advice on open-ended rows names DateRange and LocalDateRange but not YearMonthRange. Document it beside them, or read infinity) as an unbounded month end if the month-alignment rule allows.

Done when

A foreign nested generic argument gives the intended message (test), and docs/efcore.md says what a YearMonthRange column does with an exclusive infinity) (with a claim held by a live test).