ci: add static analysis, sanitizers, and formatting enforcement

Add Tier 1 review automation to catch issues before human review:

- Add cppcheck and clang-format to CI lint job
- Add sanitizer matrix (ASan + TSan) CI job
- Enable -Wextra -Wpedantic -Werror in CI build
- Add SANITIZER and STRICT_WARNINGS CMake options
- Add .clang-format for consistent code style
- Update Dockerfile with cppcheck and clang-format
- Fix sign-compare and unused-parameter warnings for -Werror

src/shared/compression.c

@@ -7,6 +7,7 @@
 #define INITIAL_DECOMPRESS_BUF_SIZE (1024 * 1024)
 
 Data *data_compress(Data *data_to_compress, int compression_level) {
+  (void)compression_level;
   log_message(LOG_LEVEL_DEBUG, "Starting to compress data");
   size_t dst_size = ZSTD_compressBound(data_to_compress->size);
   Data *compressed_data = data_create_empty(dst_size);

src/shared/file.c

@@ -235,7 +235,7 @@ bool file_send_sendfile(File *file, int file_descriptor, bool use_metadata, bool
   }
 
   off_t offset = 0;
-  while (offset < file_size) {
+  while ((unsigned long long)offset < file_size) {
     ssize_t sent = sendfile(file_descriptor, fd, &offset, file_size - offset);
     if (sent == -1) {
       perror("sendfile failed");

src/shared/protocol.c

@@ -68,7 +68,7 @@ bool send_n_data(int file_descriptor, void *data, size_t data_size) {
   log_message(LOG_LEVEL_DEBUG, "    Sending n Data: %zu", data_size);
   int fd = io_fd(io_write_fd, file_descriptor);
   ssize_t total_bytes_send = 0;
-  while (total_bytes_send < data_size) {
+  while ((size_t)total_bytes_send < data_size) {
     size_t chunk = data_size - total_bytes_send;
     if (io_bwlimit > 0 && chunk > 65536)
       chunk = 65536;