set Cargo feature resolver to v2 (#8917)

* fix: version of Cargo feature resolver.

This commit solve the ambiguity to determin the version of resolver.
To get more detail, see the following two documents:

- https://doc.rust-lang.org/cargo/reference/resolver.html#resolver-versions
- https://doc.rust-lang.org/edition-guide/rust-2021/default-cargo-resolver.html

* unified: Rust edition in all workspaces.

Now, the Rust 2021 is available in all workspaces.

* fined up: Cargo.toml by using workspace inheritance.

To get more detail of the `workspace.package` table, see a following document:

- https://doc.rust-lang.org/cargo/reference/workspaces.html#the-package-table

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