[CaffeinatedCoder]

Closes #231

Problem

UnassignedNoDefaultMemberAnalyzer.Assignments.Collect recorded a property assignment only on a bare IInstanceReferenceOperation and added the referenced property. A class reaches its own explicit interface implementation only through a cast, ((IHasId)this).Id = id: its Instance is a conversion over this, and its property is IHasId.Id, not the class's implementation that is the candidate. So CMTK0006 reported a member every constructor assigns, which fails a warnings-as-errors build.

Change

• UnassignedNoDefaultMemberAnalyzer.cs: Collect strips conversions down to this, for fields and properties, and maps an interface's property to the analysed type's implementation (FindImplementationForInterfaceMember). Tuple elements and ref/out arguments go through the same Collect. A local holding this is not followed: IHasId self = this; self.Id = id; stays reported (the issue left this to the fix; the README says so).
• Sibling (Found-By: VA, its own commit): Collect took any instance reference as this, so a constructor whose only assignment was new Twin(0) { Id = x } or other with { Id = x } counted as assigning its own Id, and CMTK0006 was silent. Only the containing instance counts now.
• Analyzers README: the CMTK0006 section says the cast counts and the alias doesn't; claim K06-an-explicit-implementation-through-a-cast holds it. Remarks on the analyzer updated.
• CHANGELOG under 2.3.1: the fix under ### Fixed, the sibling under ### Changed since a warnings-as-errors build can now fail. Both are a Warning, so no exception to decision 34.

Tests

• A_member_assigned_through_a_cast_of_this_stays_silent, across the forms that assign a member in a constructor: this., a cast of this to an interface the member implements explicitly, implicitly, to the second of two, to a generic one, a cast to the class itself (field), deconstruction through the cast, and out through the cast. All seven were reported before.
• A_cast_assigns_only_the_member_it_reaches_on_this: two constructors where only one assigns through the cast name the other; a cast of another instance assigns nothing; a local alias stays reported.
• An_initializer_of_another_instance_assigns_nothing_on_this: an object initializer and a with of another instance report.
• Reverting the source fails all three; keeping the interface's property instead of mapping it fails the first two; reverting the sibling fails its row (0 reports where 2 are expected).
• Analyzers (3,692), Conventions (2,016), Samples (150) and Oracles (51) green locally through tools/BuildVerdict; the solution builds clean.

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