Edition cleanup

Some cleanup to follow the language updates, new clippy lints and Rust 2021.

The crate duniter-gva-gql could not be migrated to 2021, probably because of an async_graphql's macro.

&[T]::try_into() -> [T; N] is simpler and safer than using uninit.

bda/Cargo.toml

@@ -3,7 +3,7 @@ name = "duniter-bda"
 version = "0.1.0"
 authors = ["librelois <elois@duniter.org>"]
 license = "AGPL-3.0"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 anyhow = "1.0.33"