testing: add comprehensive test suite for test-driven development

Add unit tests for previously untested modules (protocol, data, metadata,
file, glob), robustness tests for deserialization of malformed inputs,
thread safety stress tests, property-based roundtrip tests, and 6 fuzz
targets. Update CI with CTest integration, coverage reporting, and
valgrind memory checking.

New test files:
- test_data.c: Data type lifecycle (5 tests)
- test_protocol.c: Protocol I/O roundtrips and error paths (9 tests)
- test_metadata.c: Metadata serialization roundtrips (6 tests)
- test_file.c: File operations and send/receive (12 tests)
- test_glob.c: Glob pattern matching (10 tests)
- test_robustness.c: Malformed input handling for chunk/delta/protocol (11 tests)
- test_stress.c: MPMC queue stress, backpressure, rapid create/destroy (3 tests)
- test_property.c: Compress, delta, chunk, glob roundtrip properties (4 tests)
- tests/fuzz/: 6 libFuzzer targets for deserialization functions

Extended existing tests:
- test_config.c: config_send/config_receive roundtrip via fork+pipe
- test_shared_utils.c: mkdir_r, glob_match, delete_extras

Infrastructure:
- CTest integration in CMakeLists.txt
- Coverage support (-DENABLE_COVERAGE=ON)
- Fuzz target support (-DENABLE_FUZZ=ON)
- CI: coverage, valgrind, address sanitizer jobs
- Fixed MPMC stress test race condition (cnd_signal -> cnd_broadcast)

tests/runner.c

@@ -2,10 +2,18 @@
 #include "test_chunk.h"
 #include "test_compression.h"
 #include "test_config.h"
+#include "test_data.h"
 #include "test_delta.h"
+#include "test_file.h"
+#include "test_glob.h"
+#include "test_metadata.h"
+#include "test_property.h"
+#include "test_protocol.h"
 #include "test_queue.h"
+#include "test_robustness.h"
 #include "test_scanner.h"
 #include "test_shared_utils.h"
+#include "test_stress.h"
 #include "test_utils.h"
 #include <stdio.h>
 
@@ -25,6 +33,14 @@ int main() {
   RUN_TEST(test_compression);
   RUN_TEST(test_scanner);
   RUN_TEST(test_delta);
+  RUN_TEST(test_data);
+  RUN_TEST(test_protocol);
+  RUN_TEST(test_metadata);
+  RUN_TEST(test_glob);
+  RUN_TEST(test_file);
+  RUN_TEST(test_robustness);
+  RUN_TEST(test_stress);
+  RUN_TEST(test_property);
 
   printf("\n\033[1;36m=== TEST SUMMARY ===\033[0m\n");
   printf("Total Tests Run: %d\n", tests_run);