chore: pin toolchain to MSRV(1.76) (#900)

* chore: pin toolchain to MSRV(1.76)

* chore: remove more toolchain action & update readme

.github/workflows/ci.yml

@@ -7,7 +7,6 @@ on:
 name: CI
 
 env:
-  RUST_VER: 'stable'
   CROSS_VER: '0.2.5'
   CARGO_NET_RETRY: 3
 
@@ -19,12 +18,6 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
-      - name: Setup Rust
-        uses: dtolnay/rust-toolchain@master
-        with:
-          toolchain: '${{ env.RUST_VER }}'
-          components: rustfmt
-
       - name: Run cargo fmt
         env:
           TERM: xterm-256color
@@ -73,12 +66,6 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
-      - name: Setup Rust
-        uses: dtolnay/rust-toolchain@master
-        with:
-          toolchain: '${{ env.RUST_VER }}'
-          components: clippy
-
       - name: Setup Rust Cache
         uses: Swatinem/rust-cache@v2
         with: