Incorrect copyright headers

[Adamantios]

The copyright is incorrect in multiple files.

This was not detected because the CI does not check the copyright correctly here.

[Devanshusisodiya]

@Adamantios The copyright info for example in the file should be updated to Copyright 2024 Valory AG and similarly everywhere?

[Adamantios]

@Devanshusisodiya no, the copyright of a file should have a range specifying when it was created and when it was last updated, or a single number if the year of creation and last update are the same.

The linked command on the CI above should be replaced with:

run: tomte check-copyright --author valory --author fetchai

Running this locally should also give hints on what the copyright issues currently are.

[Devanshusisodiya]

@Adamantios I have raised this PR to fix this issue, please review and comment. Thanks.