chore(test): support custom cargo target directories

Some users may change their "target-dir" cargo setting for example to
make it shared between all projects (may speed up some builds).
It that case our integration tests should be looking for the executable
in the right place.

test/conftest.py

 import io
+import json
 import os
 import re
 import sys
@@ -533,7 +534,9 @@ def compile() -> None:
 
 @pytest.fixture(scope="session")
 def binary_path(compile, pytestconfig) -> str:
-    return os.path.realpath(pytestconfig.rootpath / "target/debug/picodata")
+    metadata = subprocess.check_output(["cargo", "metadata", "--format-version=1"])
+    target = json.loads(metadata)["target_directory"]
+    return os.path.realpath(os.path.join(target, "debug/picodata"))
 
 
 @pytest.fixture(scope="session")