Update copyright notices

[gligneul]

📚 Context

Hey all, to more closely align with the reality that Cartesi is built by an ever-growing ecosystem of independent contributors -- and in order to bring recognition to the copyrighted contributions of individual authors -- the recommended course of action for copyright notices in all official Cartesi Github repositories is as follows:

• All existing copyright notices pertaining to code written by Cartesi contributors that is licensed under Apache 2.0 should be changed to:

(c) Cartesi and individual authors (see AUTHORS)
SPDX-License-Identifier: Apache-2.0 (see LICENSE)

• All existing copyright notices pertaining to code written by Cartesi contributors that is licensed under LGPL-3.0 should be changed to:

(c) Cartesi and individual authors (see AUTHORS)
SPDX-License-Identifier: LGPL-3.0 (see LICENSE)

• No year is needed for any copyright notice.

• Each repository should contain an AUTHORS file. Any contributor who has in the past had at least one pull request for a code change accepted in that repo may submit a pull request to have their name added to the AUTHORS file. Submissions to the AUTHORS file should be in the format:

Name <email>

In the first instance, the individual contributor(s) responsible for approving pull requests for that repo will need to manually check that the author submitting their name for inclusion previously had a pull request for a code change accepted in that repo. Contributors may then seek a way to automate this process moving forward.

Inclusion in the AUTHORS file for each repo is entirely voluntary. It is up to each individual author to decide whether they would like attribution in a given AUTHORS file and to submit a pull request accordingly. Please note that a contributor's decision on whether to seek attribution in an AUTHORS file will have no impact on copyright ownership.

See https://discord.com/channels/600597137524391947/1130905237901803560/1131962825695297567

[gligneul]

We should add instructions regarding AUTHORS in the CONTRIBUTING.md file.