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

errors.hpp

@@ -1,3 +1,6 @@
+#ifndef ERRORS_HPP
+#define ERRORS_HPP
+
 #define EXIT_INCOMPLETE 100
 #define EXIT_ARGS 101
 #define EXIT_CLOSE 102
@@ -21,3 +24,36 @@
 #define EXIT_WRITE 120
 
 // avoid 124, 125, 126, 127, 137, which are used by GNU timeout
+
+#include <stdexcept>
+#include <string>
+#include <exception>
+
+class tippecanoe_error : public std::runtime_error {
+       public:
+	int exit_code;
+	tippecanoe_error(int code, const std::string &message)
+	    : std::runtime_error(message), exit_code(code) {
+	}
+};
+
+// Format and throw a tippecanoe_error. Use in place of fprintf(stderr,...)+exit().
+[[noreturn]] void throw_tippecanoe_error(int code, const char *fmt, ...)
+	__attribute__((format(printf, 2, 3)));
+
+// Throw from errno-based errors (replaces perror()+exit() pattern)
+[[noreturn]] void throw_perror(int code, const char *msg);
+
+// Check the void* return value from pthread_join. If a thread caught an
+// exception, the return value is a heap-allocated std::exception_ptr.
+// This re-throws it on the joining thread, or does nothing if retval is NULL.
+inline void rethrow_if_thread_failed(void *retval) {
+	if (retval != NULL) {
+		std::exception_ptr *ep = (std::exception_ptr *) retval;
+		std::exception_ptr copy = *ep;
+		delete ep;
+		std::rethrow_exception(copy);
+	}
+}
+
+#endif