Add codecov and remove Travis + Appveyor config (#156)

Author: devmotion

.codecov.yml

@@ -37,3 +37,9 @@ jobs:
       - uses: julia-actions/cache@v2
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
+      - uses: julia-actions/julia-processcoverage@v1
+      - uses: codecov/codecov-action@v5
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }} # required
+          fail_ci_if_error: true
+          files: ./lcov.info