chore: migrate ruff config to [lint] and enforce top-level imports (#140)

Author: kishore7snehil

.ruff.toml

@@ -1,5 +1,7 @@
 line-length = 100
 target-version = "py39"
+
+[lint]
 select = [
     "E",   # pycodestyle errors
     "W",   # pycodestyle warnings
@@ -9,8 +11,9 @@ select = [
     "C4",  # flake8-comprehensions
     "UP",  # pyupgrade
     "S",   # bandit (security)
+    "PLC0415",  # import outside top level
 ]
 ignore = ["E501", "B904"]  # Line too long (handled by black), Exception handling without from
 
-[per-file-ignores]
+[lint.per-file-ignores]
 "tests/*" = ["S101", "S105", "S106"]  # Allow assert and ignore hardcoded password warnings in test files