Add Foundry tests to coverage (#5098)

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>

scripts/checks/coverage.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+export COVERAGE=true
+export FOUNDRY_FUZZ_RUNS=10
+
+# Hardhat coverage
+hardhat coverage
+
+if [ "${CI:-"false"}" == "true" ]; then
+  # Foundry coverage
+  forge coverage --report lcov
+  # Remove zero hits
+  sed -i '/,0/d' lcov.info
+fi
+
+# Reports are then uploaded to Codecov automatically by workflow, and merged.