[Bug]: GenerateAssertion drops parameter default values from generated extension method

[ascott18]

Description

The following code is a compilation error because the source generated extension method has lost the true default value of the exact parameter.

public class UnitTest1
{
    [Test]
    public async Task TestWithMemberData()
    {
        string[] items = new[] { "food", "bard" };
        await Assert.That(items).ContainsMessage("foo"); // ERROR: parameter `bool exact` expected
    }
}

public static partial class Assertions
{
    [EditorBrowsable(EditorBrowsableState.Never)]
    [GenerateAssertion(ExpectationMessage = "to contain message '{needle}'")]
    public static bool ContainsMessage(this IEnumerable<string> strings, string needle, bool exact = true)
    {
        return strings.Any(x => exact ? x == needle : x.Contains(needle));
    }
}

Expected Behavior

Source generated extension preserves parameter defaults.

Actual Behavior

Parameter defaults lost

Steps to Reproduce

See above code

TUnit Version

1.15.0

.NET Version

NET 10

Operating System

Windows

IDE / Test Runner

dotnet CLI (dotnet test / dotnet run)

Error Output / Stack Trace

Additional Context

No response

IDE-Specific Issue?

• I've confirmed this issue occurs when running via dotnet test or dotnet run, not just in my IDE