--retain-equatable-properties option

[pm-dev]

In tests, we may want to use an Equatable to verify two structs are equal (or two arrays of equatable structs):

struct Mock {

  struct Args: Equatable {
      let param1: String
  }

  var invocations: [Args] = []

  func callFunction(param1: String) {
    invocations.append(Args(param1: param1))
  }
}

// Then in tests

#expect(mock.invocations == expectedInvocations)

Periphery will identify param1 as assigned but never used if it's only used for this purpose. Would be nice to have a --retain-equatable-properties flag similar to --retain-codable-properties