Add initial nistec project files

internal/fiat/p256_extra.go

@@ -0,0 +1,12 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fiat
+
+// Bits returns a reference to the underlying little-endian fully-reduced
+// Montgomery representation of e. Handle with care.
+func (e *P256Element) Bits() *[4]uint64 {
+	var _ p256MontgomeryDomainFieldElement = e.x
+	return (*[4]uint64)(&e.x)
+}