Throw instead of exiting from the tile clipping and overzooming code

The code reachable from overzooming a tile no longer calls exit(). It
reports errors by throwing tippecanoe_error, and owns its FILE * and
json_pull * handles through RAII wrappers so that nothing leaks when an
error unwinds the stack.

New files:

* errors.hpp/errors.cpp: the tippecanoe_error exception class, plus
  throw_tippecanoe_error() and throw_perror() helpers.
* raii.hpp: unique_file and unique_json_pull, both std::unique_ptr
  aliases, for FILE * and json_pull *.

exit() becomes throw in clip.cpp, mvt.cpp, mvt.hpp, read_json.cpp,
evaluator.cpp, text.cpp, geometry.cpp, attribute.cpp, and
write_json.hpp. Each tool's main() is now a try/catch around an
inner_main(), so the command-line tools exit with the status they
always did.

Along the way this fixes a z_stream leaked when compress() failed, an
exit() that could run from json_writer's destructor during unwinding,
and an exit() in mvt_value's hash function.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DuCSVGssWNUCpVEE8Yp5HT

decode.cpp

@@ -589,7 +589,7 @@ void usage(char **argv) {
 	exit(EXIT_ARGS);
 }
 
-int main(int argc, char **argv) {
+int inner_main(int argc, char **argv) {
 	extern int optind;
 	extern char *optarg;
 	int i;
@@ -666,3 +666,15 @@ int main(int argc, char **argv) {
 
 	return 0;
 }
+
+int main(int argc, char **argv) {
+	try {
+		return inner_main(argc, argv);
+	} catch (tippecanoe_error &e) {
+		fprintf(stderr, "%s\n", e.what());
+		return e.exit_code;
+	} catch (std::exception &e) {
+		fprintf(stderr, "Error: %s\n", e.what());
+		return EXIT_FAILURE;
+	}
+}