Document NUnit Result inference limitation and typed assertion solution

[Copilot]

should equal accepts the actual value as obj, leaving unused Result type parameters unconstrained. Identically printed values can therefore compare unequal as Result<CommitMessage, obj> and Result<CommitMessage, string>.

• Guidance: Document FsUnitTyped.shouldEqual, which links expected and actual types, and the explicit-annotation alternative. Preserve the existing DSL; requiring matching types would break assertions such as should contain.
• Regression coverage: Add cases for inferred Ok/Error type parameters and rejection of unequal payloads or cases.

open FsUnitTyped

type CommitMessage = { Type: string }

let expected: Result<_, string> = Ok { Type = "feat" }
Ok { Type = "feat" } |> shouldEqual expected

Production behavior remains unchanged.

• Fixes [NUnit] Non provided generics is inferred to obj making test fails #274