test(chain): introduce proptest for CheckPoint::range

Ensure that `CheckPoint::range` returns expected values by comparing
against values returned from a primitive approach.

I think it is a good idea to start writing proptests for this crate.

.github/workflows/cont_integration.yml

@@ -33,6 +33,7 @@ jobs:
           cargo update -p zstd-sys --precise "2.0.8+zstd.1.5.5"
           cargo update -p time --precise "0.3.20"
           cargo update -p home --precise "0.5.5"
+          cargo update -p proptest --precise "1.2.0"
       - name: Build
         run: cargo build ${{ matrix.features }}
       - name: Test