chore(internal): ensure package is importable in lint cmd (#632)

Author: stainless-app[bot]

pyproject.toml

@@ -79,10 +79,13 @@ format = { chain = [
 "lint" = { chain = [
   "check:ruff",
   "typecheck",
+  "check:importable",
 ]}
 "check:ruff" = "ruff check ."
 "fix:ruff" = "ruff check --fix ."
 
+"check:importable" = "python -c 'import anthropic'"
+
 typecheck = { chain = [
   "typecheck:pyright",
   "typecheck:mypy"