Drop the implicit List<Entity> conversion that makes three params overloads uncallable

[Rafael-SOWNet]

Entity has implicit conversions to itself from both Entity[] and List<Entity>, each building a FiniteSet. The List<Entity> one has a side effect: a list also converts to a single Entity, so for any member that has both an IEnumerable<Entity> overload and a params Entity[] overload, the params form becomes applicable in its expanded form. Neither candidate is better than the other, and the call does not compile.

var equations = new List<Entity> { "x - 1", "y - 2" };

new EquationSystem(equations);   // error CS0121: the call is ambiguous
new FiniteSet(equations);        // error CS0121
MathS.Equations(equations);      // error CS0121

This is not three separate defects. It is one conversion making every params Entity[] overload in the library uncallable with a list — including any added later.

How the three were found

Rather than fix the one I tripped over, I swept all 2602 members in PublicApi.txt for the IEnumerable<T> / T[] single-parameter overload pattern. Exactly three matched, and each was then confirmed by compiling the call in isolation:

call shape	before	after
new EquationSystem(list)	CS0121	OK
new FiniteSet(list)	CS0121	OK
MathS.Equations(list)	CS0121	OK
the same three with Entity[]	OK	OK
the same three with IEnumerable<Entity>	OK	OK
the same three variadic	OK	OK

Only a concrete List<Entity> ever broke — an array, an IEnumerable<Entity>-typed expression, and the variadic form all compiled fine. That is why it survived to a 2.0 preview.

What changes

The List<Entity> conversion is removed. The Entity[] conversion is kept: an array binds to the params overload in its normal form by an identity conversion, which wins outright, so it never produced the ambiguity.

Entity set = new List<Entity> { 1, 2, 3 };            // no longer compiles
Entity set = new List<Entity> { 1, 2, 3 }.ToSet();    // use this
Entity set = new Entity[] { 1, 2, 3 };                // unchanged

Breaking, so it wants the 2.0 window — recorded in BREAKING-CHANGES.md, and PublicApi.txt updated.

Regression guard

ListArgumentOverloadTest calls all three members with a List<Entity>. The guard is that the test project compiles — restore the conversion and the build breaks, which a runtime assertion could not catch. Sources/.editorconfig gets a per-file header section for the new file, since Tests/UnitTests/Common still carries the 2022 template and IDE0073 is an error.

Verification

• 6055 C# tests pass, 0 failed, 14 skipped
• 130 F# wrapper tests pass
• library, F# wrapper and Utils build clean
• all ten call shapes in the matrix above compile

The two NETSDK1100 failures in a full solution build are the WinForms/WPF sample projects, which cannot build on Linux; unrelated to this change.

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