feat: add serial port listing and CLI flags

Implement cel_serial_list_ports/cel_serial_free_ports with
platform backends: Windows reads HKLM\HARDWARE\DEVICEMAP\
SERIALCOMM (fast, single registry read), POSIX scans /dev for
ttyUSB*/ttyACM*.

telemetry tool gains --list, --port, and --baudrate flags;
baud rate was previously hardcoded to 400000. Rename the
tool_telemetry CMake target to telemetry.

Fix test_free_ports_zero_count, which passed a stack array to
cel_serial_free_ports (which calls free() on it), corrupting
the heap.

tools/CMakeLists.txt

@@ -1,4 +1,4 @@
-add_executable(tool_telemetry telemetry.c)
-target_include_directories(tool_telemetry PRIVATE "${CMAKE_SOURCE_DIR}")
-target_compile_features(tool_telemetry PRIVATE c_std_23)
-target_link_libraries(tool_telemetry PRIVATE celrs_crsf celrs_serial celrs_logger celrs_log_write)
+add_executable(telemetry telemetry.c)
+target_include_directories(telemetry PRIVATE "${CMAKE_SOURCE_DIR}")
+target_compile_features(telemetry PRIVATE c_std_23)
+target_link_libraries(telemetry PRIVATE celrs_crsf celrs_serial celrs_logger celrs_log_write)

tools/telemetry.c

@@ -32,33 +32,63 @@ static int telemetry_parse_link(int16_t* rssi, uint8_t* link_quality,
 }
 
 static void print_usage(char const* prog) {
-    printf("Usage: %s <serial_port> [interval_ms]\n", prog);
-    printf("  serial_port  : COM3 (Windows) or /dev/ttyUSB0 (Linux)\n");
-    printf("  interval_ms  : poll interval in ms (default 200)\n");
+    printf("Usage: %s --port <serial_port> [--baudrate <rate>] [interval_ms]\n", prog);
+    printf("       %s --list\n", prog);
+    printf("  --port <serial_port> : COM3 (Windows) or /dev/ttyUSB0 (Linux)\n");
+    printf("  --baudrate <rate>    : baud rate (default 400000)\n");
+    printf("  interval_ms          : poll interval in ms (default 200)\n");
+    printf("  --list               : list available serial ports and exit\n");
+}
+
+static int list_ports(void) {
+    char** ports = NULL;
+    int count = cel_serial_list_ports(&ports, 0);
+    if (count < 0) {
+        cel_log_err("Failed to list serial ports");
+        return 1;
+    }
+
+    for (int i = 0; i < count; i++) {
+        printf("%s\n", ports[i]);
+    }
+
+    cel_serial_free_ports(ports, count);
+    return 0;
 }
 
 int main(int argc, char const* argv[]) {
-    if (argc < 2) {
+    char const* port_path = NULL;
+    int baud_rate = 400000;
+    int interval_ms = 200;
+
+    for (int i = 1; i < argc; i++) {
+        if (strcmp(argv[i], "--list") == 0) {
+            return list_ports();
+        } else if (strcmp(argv[i], "--port") == 0 && i + 1 < argc) {
+            port_path = argv[++i];
+        } else if (strcmp(argv[i], "--baudrate") == 0 && i + 1 < argc) {
+            baud_rate = atoi(argv[++i]);
+            if (baud_rate <= 0) baud_rate = 400000;
+        } else {
+            interval_ms = atoi(argv[i]);
+            if (interval_ms <= 0) interval_ms = 200;
+        }
+    }
+
+    if (port_path == NULL) {
         print_usage(argv[0]);
         return 1;
     }
 
-    char const* port_path = argv[1];
-    int interval_ms = 200;
-    if (argc >= 3) {
-        interval_ms = atoi(argv[2]);
-        if (interval_ms <= 0) interval_ms = 200;
-    }
-
     /* Open serial port */
-    cel_serial_port* port = cel_serial_open(port_path, 400000);
+    cel_serial_port* port = cel_serial_open(port_path, baud_rate);
     if (port == NULL) {
         cel_log_err("Failed to open serial port");
         return 1;
     }
 
     char msg[256];
-    snprintf(msg, sizeof(msg), "Connected to %s (400000 baud)", port_path);
+    snprintf(msg, sizeof(msg), "Connected to %s (%d baud)", port_path, baud_rate);
     cel_log_info(msg);
 
     /* Send heartbeat to establish CRSF link */