docs: Update license year to 2024

[joshka]

This removes the copyright year in all the LICENSE files. It also uses the MIT license text with the wrapping from https://choosealicense.com/licenses/mit/ rather than the more narrow wrapped text that was previously used, and adds the explicit "MIT License" header to each file to make this more obvious.

Motivation

When I opened the license file, I was unsure if this was MIT licensed or another custom license due to the lack of header and non-standard formatting.

Solution

Use a more standard formatted license, and ensure the header states this is an MIT License.

[joshka]

See also comments in related PR for Tokio https://github.com/tokio-rs/tokio/pull/6451