Add ruff (lint + format) and ty (type checking) to the project

Adds [tool.ruff] and [tool.ty] config to pyproject.toml with a curated
ruff rule set (E, F, W, I, UP, B, C4, SIM, RUF, ASYNC, LOG, G, PIE, RET,
PERF, N), pins ruff/ty in requirements-dev.txt, reformats the whole tree
with `ruff format`, and fixes the pre-existing lint and type-check debt
those tools surfaced so both run clean.

Production-code type fixes include: HA's ConfigFlowResult vs. the
generic FlowResult in config_flow.py, narrowing BoundEntity.desc to its
platform-specific subclass (SelectDesc/NumberDesc/SensorDesc/etc.) via
cast() instead of an unchecked annotation, converting HA device_class
strings to their proper enum types, a resolve_registry callback typed
as `object` instead of `DeviceRegistry | None`, and a couple of other
narrow correctness fixes (CA key type validation, an index-out-of-bounds
false positive from an empty-tuple fallback, a bool/dict argument swap).

Test-file fixes are mechanical: narrowing SamsungEntityDescription to
the correct subclass via isinstance()/cast() before accessing
subclass-only fields, and asserting Optional write_fn/unit_fn fields
are set before calling them.

tests/test_fridge_multi_instance.py

@@ -5,31 +5,32 @@ ice-maker resources (/icemaker/one/vs/0, /icemaker/two/vs/0) use named path
 segments rather than numeric indices, so they are modelled via DOOR_GENERIC
 pattern capability that auto-derives distinct keys from the href segments.
 """
-from tests.conftest import _load_resources
 
 from custom_components.localthings.registry.adapter import _key
 from custom_components.localthings.registry.by_type import refrigerator
 from custom_components.localthings.registry.discovery import discover
+from tests.conftest import _load_resources
 
 
 def test_two_doors_get_distinct_keys():
-    resources = _load_resources('10.0.0.254')
+    resources = _load_resources("10.0.0.254")
     reg = refrigerator.REGISTRY
     bound = discover(resources, reg.capabilities, reg.pattern_capabilities)
-    door_keys = sorted(_key(b) for b in bound if _key(b).startswith('door'))
+    door_keys = sorted(_key(b) for b in bound if _key(b).startswith("door"))
     # at least the two physical doors (cooler + freezer) produce distinct keys
     assert len(set(door_keys)) >= 2, f"Expected >= 2 distinct door keys, got: {door_keys}"
 
 
-def test_two_iceMakers_get_distinct_keys():
-    resources = _load_resources('10.0.0.254')
+def test_two_ice_makers_get_distinct_keys():
+    resources = _load_resources("10.0.0.254")
     reg = refrigerator.REGISTRY
     bound = discover(resources, reg.capabilities, reg.pattern_capabilities)
-    ice_keys = sorted(_key(b) for b in bound if _key(b).startswith('icemaker_'))
+    ice_keys = sorted(_key(b) for b in bound if _key(b).startswith("icemaker_"))
     # icemaker_one_* and icemaker_two_* are distinct
-    ice_one_keys = [k for k in ice_keys if k.startswith('icemaker_one_')]
-    ice_two_keys = [k for k in ice_keys if k.startswith('icemaker_two_')]
+    ice_one_keys = [k for k in ice_keys if k.startswith("icemaker_one_")]
+    ice_two_keys = [k for k in ice_keys if k.startswith("icemaker_two_")]
     assert ice_one_keys, "No icemaker_one_* keys found"
     assert ice_two_keys, "No icemaker_two_* keys found"
-    assert set(ice_one_keys).isdisjoint(set(ice_two_keys)), \
+    assert set(ice_one_keys).isdisjoint(set(ice_two_keys)), (
         f"icemaker_one and icemaker_two keys overlap: {ice_one_keys} vs {ice_two_keys}"
+    )