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/fuzz/fuzz_glob_match.c

@@ -0,0 +1,32 @@
+#include "utils.h"
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  if (size < 2)
+    return 0;
+
+  // Split input into pattern and string at the midpoint
+  size_t mid = size / 2;
+
+  char* pattern = malloc(mid + 1);
+  char* str = malloc(size - mid + 1);
+  if (!pattern || !str) {
+    free(pattern);
+    free(str);
+    return 0;
+  }
+
+  memcpy(pattern, data, mid);
+  pattern[mid] = '\0';
+
+  memcpy(str, data + mid, size - mid);
+  str[size - mid] = '\0';
+
+  glob_match(pattern, str);
+
+  free(pattern);
+  free(str);
+  return 0;
+}