chore: pin rust nightly version

Author: jlucaso1

.github/workflows/benchmark.yml

@@ -21,7 +21,9 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: dtolnay/rust-toolchain@nightly
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: nightly-2025-12-19
 
       - name: Install protoc
         uses: taiki-e/install-action@v2

.github/workflows/copilot-setup-steps.yml

@@ -19,12 +19,12 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Set up Rust
-        uses: dtolnay/rust-toolchain@nightly
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: nightly-2025-12-19
 
       - name: Cache Rust dependencies
         uses: Swatinem/rust-cache@v2
-        with:
-          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
 
       - name: Fetch Rust dependencies
         run: cargo fetch

.github/workflows/main.yml

@@ -18,8 +18,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@nightly
+      - uses: dtolnay/rust-toolchain@master
         with:
+          toolchain: nightly-2025-12-19
           components: rustfmt
       - run: cargo fmt --all -- --check
 
@@ -28,17 +29,16 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@nightly
+      - uses: dtolnay/rust-toolchain@master
         with:
+          toolchain: nightly-2025-12-19
           components: clippy
       - name: Install protoc
         uses: taiki-e/install-action@v2
         with:
           tool: protoc@${{ env.PROTOC_VERSION }}
       - name: Cache Rust dependencies
         uses: Swatinem/rust-cache@v2
-        with:
-          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
       - name: Run Clippy
         run: cargo clippy --all-targets -- -D warnings
 
@@ -47,15 +47,15 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@nightly
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: nightly-2025-12-19
       - name: Install protoc
         uses: taiki-e/install-action@v2
         with:
           tool: protoc@${{ env.PROTOC_VERSION }}
       - name: Cache Rust dependencies
         uses: Swatinem/rust-cache@v2
-        with:
-          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
       - name: Build project
         run: cargo build --all-targets --verbose
       - name: Run tests