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/pipes/bool_pipe_test.py

@@ -0,0 +1,36 @@
+import pytest
+from cpl.core.pipes.bool_pipe import BoolPipe
+
+
+def test_to_str_true():
+    assert BoolPipe.to_str(True) == "true"
+
+
+def test_to_str_false():
+    assert BoolPipe.to_str(False) == "false"
+
+
+def test_from_str_true_values():
+    assert BoolPipe.from_str("True") is True
+    assert BoolPipe.from_str("true") is True
+    assert BoolPipe.from_str("1") is True
+    assert BoolPipe.from_str("yes") is True
+    assert BoolPipe.from_str("y") is True
+    assert BoolPipe.from_str("Y") is True
+
+
+def test_from_str_false_values():
+    assert BoolPipe.from_str("false") is False
+    assert BoolPipe.from_str("False") is False
+    assert BoolPipe.from_str("0") is False
+    assert BoolPipe.from_str("no") is False
+    assert BoolPipe.from_str("") is False
+    assert BoolPipe.from_str("anything") is False
+
+
+def test_roundtrip_true():
+    assert BoolPipe.from_str(BoolPipe.to_str(True)) is True
+
+
+def test_roundtrip_false():
+    assert BoolPipe.from_str(BoolPipe.to_str(False)) is False