Add analyzer rule for ArgumentException.ThrowIfContainsDuplicates #728

Summary

NetEvolve.Arguments provides ArgumentException.ThrowIfContainsDuplicates(IEnumerable<T>, IEqualityComparer<T>?) to validate that a collection contains no duplicate elements. NetEvolve.Arguments.Analyser does not currently have a rule that detects the manual equivalent of this check.

Problem

The manual implementation of a duplicate check is a multi-statement algorithm rather than a single expression, e.g.:

var set = new HashSet<T>();
foreach (var item in arg)
{
    if (!set.Add(item))
    {
        throw new ArgumentException("The collection cannot contain duplicate elements.", nameof(arg));
    }
}

or the LINQ equivalent:

if (arg.Distinct().Count() != arg.Count())
{
    throw new ArgumentException(nameof(arg));
}

Because this spans a loop/multiple statements (not a single if (condition) throw ... expression) and has many equivalent formulations, it doesn't fit the single-expression pattern-matching approach used by the current rules and needs a dedicated design (e.g. matching on a HashSet<T>-based loop shape, or restricting scope to specific LINQ-based idioms).

Proposed solution

Design and implement a new rule (next available ID) that recognizes at least the most common LINQ-based shape (e.g. arg.Distinct().Count() != arg.Count() / .GroupBy(...).Any(g => g.Count() > 1)), with a code fix rewriting to ArgumentException.ThrowIfContainsDuplicates(arg). If reliable detection isn't feasible, document that decision and close as won't-fix.

References

• ArgumentExceptionPolyfill.cs — ThrowIfContainsDuplicates implementation
• src/NetEvolve.Arguments.Analyser — existing analyzer rules and test harness
• Related PR: feat(analyser): add NetEvolve.Arguments.Analyser project #724