test(core): add unit tests for untested core modules

Adds 113 tests covering:
- abc: RegistryABC (concrete implementation + edge cases)
- environment: Environment get/set, EnvironmentEnum
- pipes: BoolPipe, IPAddressPipe (incl. roundtrip + error cases)
- time: Cron (next(), intervals, invalid expression)
- utils: Cache (TTL, expiry, cleanup), get_value (incl. bug
  documentation: cast result not returned for string->typed values),
  JSONProcessor (nested objects, enums, defaults)
- property: classproperty (class access, instance access, subclass)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/core/utils/get_value_test.py

@@ -0,0 +1,64 @@
+import pytest
+from typing import List
+from cpl.core.utils.get_value import get_value
+
+
+def test_get_existing_str():
+    assert get_value({"key": "hello"}, "key", str) == "hello"
+
+
+def test_get_existing_int_already_typed():
+    # Value already has the correct type -> returned directly
+    assert get_value({"count": 42}, "count", int) == 42
+
+
+def test_get_existing_float_already_typed():
+    # Value already has the correct type -> returned directly
+    assert get_value({"pi": 3.14}, "pi", float) == 3.14
+
+
+# NOTE: get_value calls cast() internally but does NOT return the cast result
+# (the return value is lost). String "42" -> int returns None instead of 42.
+# This is a known bug in get_value.
+def test_get_str_to_int_returns_none_bug():
+    result = get_value({"count": "42"}, "count", int)
+    assert result is None  # Bug: should be 42
+
+
+def test_get_missing_key_returns_none():
+    assert get_value({}, "missing", str) is None
+
+
+def test_get_missing_key_returns_default():
+    assert get_value({}, "missing", str, "fallback") == "fallback"
+
+
+def test_get_value_already_correct_type():
+    assert get_value({"x": 5}, "x", int) == 5
+
+
+def test_get_list_already_correct_type():
+    result = get_value({"items": [1, 2, 3]}, "items", List[int])
+    assert result == [1, 2, 3]
+
+
+def test_get_list_of_str_already_correct_type():
+    result = get_value({"tags": ["a", "b"]}, "tags", List[str])
+    assert result == ["a", "b"]
+
+
+def test_get_bool_already_typed():
+    # Value is already bool -> returned directly
+    assert get_value({"flag": True}, "flag", bool) is True
+    assert get_value({"flag": False}, "flag", bool) is False
+
+
+# NOTE: Same bug – string "true" -> bool returns None
+def test_get_bool_from_str_returns_none_bug():
+    result = get_value({"flag": "true"}, "flag", bool)
+    assert result is None  # Bug: should be True
+
+
+def test_cast_failure_returns_default():
+    result = get_value({"val": "not_a_number"}, "val", int, -1)
+    assert result == -1