fix(services): name the build a compiled service is missing

A service shipped as .so/.pyd failed with a bare ModuleNotFoundError. Report the build this interpreter needs, with its version and platform.

tests/core/test_service_compiled_import_hint.py

@@ -0,0 +1,30 @@
+from __future__ import annotations
+
+from importlib.machinery import EXTENSION_SUFFIXES
+from pathlib import Path
+
+from unshackle.core.services import compiled_import_hint
+
+
+def _service(tmp_path: Path, *files: str) -> Path:
+    (tmp_path / "EXAMPLE").mkdir()
+    init = tmp_path / "EXAMPLE" / "__init__.py"
+    init.write_text("from .example import EXAMPLE\n")
+    for name in files:
+        (init.parent / name).touch()
+    return init
+
+
+def test_hint_names_the_file_this_python_needs(tmp_path: Path) -> None:
+    init = _service(tmp_path, "example.cp999-win_amd64.pyd", "example.cpython-999-x86_64-linux-gnu.so")
+    assert f"needs example{EXTENSION_SUFFIXES[0]}" in compiled_import_hint("EXAMPLE.example", init)
+
+
+def test_no_hint_when_this_python_can_load_it(tmp_path: Path) -> None:
+    init = _service(tmp_path, f"example{EXTENSION_SUFFIXES[0]}")
+    assert compiled_import_hint("EXAMPLE.example", init) == ""
+
+
+def test_no_hint_for_a_pure_python_service(tmp_path: Path) -> None:
+    init = _service(tmp_path)
+    assert compiled_import_hint("EXAMPLE.example", init) == ""