Fix crypto tests and add CI workflow

- Fixed TestNewContractAddress by using b.Bytes() in RLP encoding
- Fixed TestSaveECDSA by updating PaddedBigBytes to use FillBytes
- Added GitHub Actions workflow for testing
- All crypto package tests now passing

.github/workflows/test.yml

@@ -0,0 +1,36 @@
+name: Test
+
+on:
+  push:
+    branches: [ main, master ]
+  pull_request:
+    branches: [ main, master ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go-version: ['1.24.5']
+    
+    steps:
+    - uses: actions/checkout@v4
+    
+    - name: Set up Go
+      uses: actions/setup-go@v5
+      with:
+        go-version: ${{ matrix.go-version }}
+    
+    - name: Get dependencies
+      run: go mod download
+    
+    - name: Run tests
+      run: go test -v -race -coverprofile=coverage.txt -covermode=atomic ./...
+    
+    - name: Upload coverage to Codecov
+      uses: codecov/codecov-action@v4
+      with:
+        file: ./coverage.txt
+        flags: unittests
+        name: codecov-umbrella
+        fail_ci_if_error: false