ci: Add Foundry tooling integration test (#511)

## Description

Adds a CI workflow that builds and tests a small Foundry project with
`foundry-polkadot`'s `forge`, exercising the standard JSON interface
between `resolc` and `foundry-polkadot` end-to-end.

## Resolved Issues

Closes #513

.github/workflows/test.yml

@@ -64,6 +64,7 @@ jobs:
     outputs:
       should-run-differential-tests: ${{ steps.filter.outputs.should-run-differential-tests }}
       should-run-hardhat-tests: ${{ steps.filter.outputs.should-run-hardhat-tests }}
+      should-run-foundry-tests: ${{ steps.filter.outputs.should-run-foundry-tests }}
     steps:
       - name: Checkout
         uses: actions/checkout@v6
@@ -95,23 +96,28 @@ jobs:
 
           print_changed_files
 
+          common_ignored=(
+            '\.md$'
+            '^book/'
+            '^docs/'
+            '^js/'
+            '^package\.json$'
+            '^package-lock\.json$'
+          )
+
           echo "should-run-differential-tests=$(has_changes_other_than \
-            '\.md$' \
-            '^book/' \
-            '^docs/' \
-            '^js/' \
-            '^package\.json$' \
-            '^package-lock\.json$' \
+            "${common_ignored[@]}" \
             '^tooling-projects/' \
           )" | tee -a "$GITHUB_OUTPUT"
 
           echo "should-run-hardhat-tests=$(has_changes_other_than \
-            '\.md$' \
-            '^book/' \
-            '^docs/' \
-            '^js/' \
-            '^package\.json$' \
-            '^package-lock\.json$' \
+            "${common_ignored[@]}" \
+            '^tooling-projects/foundry' \
+          )" | tee -a "$GITHUB_OUTPUT"
+
+          echo "should-run-foundry-tests=$(has_changes_other_than \
+            "${common_ignored[@]}" \
+            '^tooling-projects/hardhat' \
           )" | tee -a "$GITHUB_OUTPUT"
 
   run-differential-tests:
@@ -123,3 +129,8 @@ jobs:
     needs: [test, check-changes]
     if: ${{ needs.check-changes.outputs.should-run-hardhat-tests == 'true' }}
     uses: ./.github/workflows/hardhat.yml
+
+  run-foundry-tests:
+    needs: [test, check-changes]
+    if: ${{ needs.check-changes.outputs.should-run-foundry-tests == 'true' }}
+    uses: ./.github/workflows/foundry.yml