feat: setup rust-toolchain.toml to use nightly by default

[LeoBorai]

Introduces rust-toolchain.toml which forces cargo to use latest Nightly.
This is useful for users using stable as the default toolchain, Rustup
responds to the presence of this file as follows:

➜  sea-query git:(master) rustup default stable
info: using existing install for 'stable-aarch64-apple-darwin'
info: default toolchain set to 'stable-aarch64-apple-darwin'

  stable-aarch64-apple-darwin unchanged - rustc 1.72.0 (5680fa18f 2023-08-23)

info: note that the toolchain 'nightly-aarch64-apple-darwin' is currently in use (overridden by '~/Repos/sea-query/rust-toolchain.toml')

[LeoBorai]

@ikrivosheev , @billy1624 not sure why we use stable for clippy and nightly for rustfmt?

sea-query/.github/workflows/rust.yml

Lines 27 to 61 in edf747b

	rustfmt:
	name: Rustfmt
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v3
	- uses: dtolnay/rust-toolchain@master
	with:
	toolchain: nightly
	components: rustfmt
	- run: cargo fmt --manifest-path Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path sea-query-attr/Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path sea-query-binder/Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path sea-query-derive/Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path sea-query-postgres/Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path sea-query-rusqlite/Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path examples/sqlx_sqlite/Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path examples/sqlx_any/Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path examples/rusqlite/Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path examples/sqlx_postgres/Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path examples/postgres/Cargo.toml --all -- --check
	- run: cargo fmt --manifest-path examples/sqlx_mysql/Cargo.toml --all -- --check
	clippy:
	name: Clippy
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v3
	- uses: dtolnay/rust-toolchain@master
	with:
	toolchain: stable
	components: clippy
	- run: cargo clippy --all-features --workspace -- -D warnings
	- run: cargo clippy --manifest-path sea-query-binder/Cargo.toml --workspace --features runtime-async-std-rustls --features=with-chrono,with-json,with-rust_decimal,with-bigdecimal,with-uuid,with-time,with-ipnetwork,with-mac_address,postgres-array -- -D warnings
	- run: cargo clippy --manifest-path sea-query-rusqlite/Cargo.toml --all-features --workspace -- -D warnings
	- run: cargo clippy --manifest-path sea-query-postgres/Cargo.toml --all-features --workspace -- -D warnings

[tyt2y3]

I think our default support target is always the latest stable.
nightly... we only needed it for cargo fmt, specifically to fmt the code in doc tests.

[LeoBorai]

Gotcha! Will se if that can be configured via the toolchain file!

[LeoBorai]

Hi @tyt2y3! After reading through rust-toolchain.toml docs and also seeking for more references, I ended up without any approach to have a Rust Toolchain setup that uses rustfmt on Nightly but Stable on other commands.

Im closing this to keep the inbox clear!