Expand test coverage for error-handling macros and error pool

Add 11 CTest programs and a shared test helper covering gaps left by the
original four tests (which only exercised FAIL/CATCH/HANDLE and CLEANUP):

- err_capture.h: capturing akerr_log_method + NDEBUG-proof AKERR_CHECK so
  tests can assert on message/status/stacktrace content, not just exit codes
- err_success: clean nested return does not break/handle/leak
- err_pool_refcount: 100k raise->catch->handle cycles leak 0 pool slots
- err_handle_default / err_handle_group / err_handle_dispatch: handler routing
- err_pass / err_ignore / err_swallow: PASS, IGNORE, FINISH(e,false)
- err_break_variants: FAIL_*_BREAK and FAIL_*_RETURN
- err_errno: system errno name lookup + "Unknown Error" boundary
- err_custom_handler: override the unhandled-error hook, assert non-fatally

Register tests via a foreach loop in CMakeLists.txt. Ignore build/.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CMakeLists.txt

@@ -44,25 +44,43 @@ target_compile_definitions(akerror
     PUBLIC AKERR_USE_STDLIB=${AKERR_USE_STDLIB}
 )
 
-add_executable(test_err_catch tests/err_catch.c)
-add_executable(test_err_cleanup tests/err_cleanup.c)
-add_executable(test_err_trace tests/err_trace.c)
-add_executable(test_err_improper_closure tests/err_improper_closure.c)
-add_test(NAME err_catch COMMAND test_err_catch)
-add_test(NAME err_cleanup COMMAND test_err_cleanup)
-add_test(NAME err_trace COMMAND test_err_trace)
-add_test(NAME err_improper_closure COMMAND test_err_improper_closure)
-
-set_tests_properties(
-    err_trace 
-    err_improper_closure 
-    PROPERTIES WILL_FAIL TRUE
+# Each test is one source file in tests/ built into test_<name> and registered
+# as CTest <name>. Tests expected to abort (unhandled error / contract
+# violation) go in AKERR_WILL_FAIL_TESTS; all others must exit 0.
+set(AKERR_TESTS
+    err_catch
+    err_cleanup
+    err_trace
+    err_improper_closure
+    err_success
+    err_pool_refcount
+    err_handle_default
+    err_handle_group
+    err_handle_dispatch
+    err_pass
+    err_ignore
+    err_swallow
+    err_errno
+    err_break_variants
+    err_custom_handler
 )
 
-target_link_libraries(test_err_catch PRIVATE akerror)
-target_link_libraries(test_err_cleanup PRIVATE akerror)
-target_link_libraries(test_err_trace PRIVATE akerror)
-target_link_libraries(test_err_improper_closure PRIVATE akerror)
+set(AKERR_WILL_FAIL_TESTS
+    err_trace
+    err_improper_closure
+)
+
+foreach(_test IN LISTS AKERR_TESTS)
+    add_executable(test_${_test} tests/${_test}.c)
+    target_include_directories(test_${_test} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/tests)
+    target_link_libraries(test_${_test} PRIVATE akerror)
+    add_test(NAME ${_test} COMMAND test_${_test})
+endforeach()
+
+set_tests_properties(
+    ${AKERR_WILL_FAIL_TESTS}
+    PROPERTIES WILL_FAIL TRUE
+)
 
 set(main_lib_dest "lib/my_library-${MY_LIBRARY_VERSION}")
 install(TARGETS akerror