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

text.cpp

@@ -8,6 +8,7 @@
 #include "milo/dtoa_milo.h"
 #include "milo/milo.h"
 #include "errors.hpp"
+#include "raii.hpp"
 
 /**
  * Returns an empty string if `s` is valid utf8;
@@ -135,7 +136,7 @@ int integer_zoom(std::string where, std::string text) {
 	double d = atof(text.c_str());
 	if (!std::isfinite(d) || d != floor(d) || d < 0 || d > 32) {
 		fprintf(stderr, "%s: Expected integer zoom level in \"tippecanoe\" GeoJSON extension, not %s\n", where.c_str(), text.c_str());
-		exit(EXIT_JSON);
+		throw_tippecanoe_error(EXIT_JSON, "%s: Expected integer zoom level in \"tippecanoe\" GeoJSON extension, not %s", where.c_str(), text.c_str());
 	}
 	return d;
 }
@@ -181,8 +182,7 @@ char *dtoa_milo(double val) {
 	std::string s = milo::dtoa_milo(val);
 	char *dup = strdup(s.c_str());
 	if (dup == NULL) {
-		perror("strdup");
-		exit(EXIT_MEMORY);
+		throw_perror(EXIT_MEMORY, "strdup");
 	}
 	return dup;
 }
@@ -191,25 +191,22 @@ char *dtoa_milo(double val) {
 std::vector<std::string> read_unidecode(const char *fname) {
 	std::string data;
 
-	FILE *f = fopen(fname, "rb");
+	unique_file f(fopen(fname, "rb"));
 	if (f == NULL) {
-		perror(fname);
-		exit(EXIT_OPEN);
+		throw_perror(EXIT_OPEN, fname);
 	}
 
 	std::string buf;
 	buf.resize(2000);
 
 	while (true) {
-		size_t nread = fread((void *) buf.c_str(), sizeof(char), buf.size(), f);
+		size_t nread = fread((void *) buf.c_str(), sizeof(char), buf.size(), f.get());
 		if (nread == 0) {
 			break;
 		}
 		data.append(buf.c_str(), nread);
 	}
 
-	fclose(f);
-
 	std::vector<std::string> out;
 	out.emplace_back();  // because the data file is 1-indexed
 	out.emplace_back();  // ascii 001