Clarify TUnit0046 diagnostic message for data source return types

[Copilot]

The TUnit0046 analyzer warns when data source methods return reference types directly instead of wrapped in Func<T>, but the diagnostic message was cryptic: "Return a Func<T> rather than a <T>"

Users couldn't understand what <T> meant or why Func<T> was required.

Changes

Updated diagnostic messages in Resources.resx:

• Title: Data source should return Func<T> for reference types
• Message: Data source method should return Func<T> for reference type parameters (other than string) to ensure proper test isolation
• Description: Added explanation that Func<T> defers object creation to prevent shared state between tests

Updated AnalyzerReleases.Shipped.md:

• Aligned documentation entry with new message format

Example

Before:

warning TUnit0046: Return a `Func<T>` rather than a `<T>`.

After:

warning TUnit0046: Data source method should return Func<T> for reference type parameters (other than string) to ensure proper test isolation

The message now explicitly states what types trigger the rule (reference types except string) and explains the rationale (test isolation).

Original prompt

---

This section details on the original issue you should resolve

<issue_title>The message in TUnit0046 is unclear.</issue_title>
<issue_description>> TUnit0046:Return a Func<T> rather than a <T>

Before reading the implementation, I didn’t really understand what TUnit0046 was asserting—why it should return a Func<T> or what <T> was referring to.

TUnit/TUnit.Analyzers/TestDataAnalyzer.cs

Lines 578 to 582 in dbe74b0

	if (!isFunc && unwrappedTypes.Any(x => x.SpecialType != SpecialType.System_String && x.IsReferenceType))
	{
	context.ReportDiagnostic(Diagnostic.Create(Rules.ReturnFunc,
	dataSourceMethod.Locations.FirstOrDefault()));
	}

After looking at the implementation, I understood that it means “when the parameter is a reference type other than string, the method should return a Func<T>.”
It might be clearer if the description explicitly stated this.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes The message in TUnit0046 is unclear. #3842

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