chore(license): append the license to the top of each file

[TarikGul]

The only place I am unsure about is adding the license to Calc. It's an apache license which is different. But it lives in the same repo. Any guidance on this would be great.

[jsdw]

The apache license header I used in scale-value, if it helps, looks like:

// Copyright (C) 2022 Parity Technologies (UK) Ltd. (admin@parity.io)
// This file is a part of the scale-value crate.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//         http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

So I just stuck that at the top of all of the .rs files.

[TarikGul]

Okay sweet this is ready for review