Migrate jsonpull to unique_ptr ownership

Replaces the shared_ptr-based json_object_ptr with a unique_ptr that
has a stateless custom deleter dispatching on json_object::type before
calling the right subclass destructor. Eliminates per-node atomic
reference-counting and the control-block allocation that shared_ptr
required for every node in the tree.

API now distinguishes owning and borrowing pointers explicitly:
- json_read / json_read_separators / json_hash_get return raw
  json_object * (borrowed from the parser-owned tree).
- json_read_tree / json_disconnect return json_object_ptr (caller
  takes ownership; back-pointers are cleared so the subtree can
  outlive the parser).
- json_free / json_context / json_stringify take raw pointers.
- The parser's container_stack holds raw pointers; jp->root keeps
  unique_ptr ownership of the most recent top-level value.

Internally, take_from_owner moves the unique_ptr out of whichever
parent vector / hash entry / parser root owned it, which both
json_free and json_disconnect rely on.

In the streaming parsers (parse_feature, parse_layers, the
geojson-loop callback), we are careful to free `j` only after we
have processed a complete Feature: json_read returns each token
as the tree is being built up, and freeing an intermediate node
would splice it out of the surrounding hash and corrupt the
in-progress feature.

Benchmark (tl_2022_us_county.json, -z0 --extend-zooms-if-still-dropping,
median of 5 runs on macOS arm64): 8.5s, vs 10.6s with shared_ptr
and 8.7s on the pre-refactor C baseline.

Co-authored-by: Cursor <cursoragent@cursor.com>

main.cpp

@@ -1215,7 +1215,7 @@ double round_droprate(double r) {
 	return std::round(r * 100000.0) / 100000.0;
 }
 
-std::pair<int, metadata> read_input(std::vector<source> &sources, char *fname, int maxzoom, int minzoom, int basezoom, double basezoom_marker_width, sqlite3 *outdb, const char *outdir, std::set<std::string> *exclude, std::set<std::string> *include, int exclude_all, json_object_ptr filter, double droprate, int buffer, const char *tmpdir, double gamma, int read_parallel, int forcetable, const char *attribution, bool uses_gamma, long long *file_bbox, long long *file_bbox1, long long *file_bbox2, const char *prefilter, const char *postfilter, const char *description, bool guess_maxzoom, bool guess_cluster_maxzoom, std::unordered_map<std::string, int> const *attribute_types, const char *pgm, std::unordered_map<std::string, attribute_op> const *attribute_accum, std::map<std::string, std::string> const &attribute_descriptions, std::string const &commandline, int minimum_maxzoom) {
+std::pair<int, metadata> read_input(std::vector<source> &sources, char *fname, int maxzoom, int minzoom, int basezoom, double basezoom_marker_width, sqlite3 *outdb, const char *outdir, std::set<std::string> *exclude, std::set<std::string> *include, int exclude_all, json_object *filter, double droprate, int buffer, const char *tmpdir, double gamma, int read_parallel, int forcetable, const char *attribution, bool uses_gamma, long long *file_bbox, long long *file_bbox1, long long *file_bbox2, const char *prefilter, const char *postfilter, const char *description, bool guess_maxzoom, bool guess_cluster_maxzoom, std::unordered_map<std::string, int> const *attribute_types, const char *pgm, std::unordered_map<std::string, attribute_op> const *attribute_accum, std::map<std::string, std::string> const &attribute_descriptions, std::string const &commandline, int minimum_maxzoom) {
 	int ret = EXIT_SUCCESS;
 
 	std::vector<struct reader> readers;
@@ -2892,7 +2892,7 @@ void set_attribute_value(const char *arg) {
 				exit(EXIT_JSON);
 			}
 
-			serial_val val = stringify_value(e.value, "json", 1, o);
+			serial_val val = stringify_value(e.value.get(), "json", 1, o.get());
 			set_attributes.emplace(e.key->string(), val);
 			i++;
 		}
@@ -2934,7 +2934,7 @@ void parse_json_source(const char *arg, struct source &src) {
 		exit(EXIT_JSON);
 	}
 
-	json_object_ptr fname = json_hash_get(o, "file");
+	json_object *fname = json_hash_get(o, "file");
 	if (fname == nullptr || fname->type != JSON_STRING) {
 		fprintf(stderr, "%s: -L%s: requires \"file\": filename\n", *av, arg);
 		exit(EXIT_JSON);
@@ -2942,17 +2942,17 @@ void parse_json_source(const char *arg, struct source &src) {
 
 	src.file = fname->string();
 
-	json_object_ptr layer = json_hash_get(o, "layer");
+	json_object *layer = json_hash_get(o, "layer");
 	if (layer != nullptr && layer->type == JSON_STRING) {
 		src.layer = layer->string();
 	}
 
-	json_object_ptr description = json_hash_get(o, "description");
+	json_object *description = json_hash_get(o, "description");
 	if (description != nullptr && description->type == JSON_STRING) {
 		src.description = description->string();
 	}
 
-	json_object_ptr format = json_hash_get(o, "format");
+	json_object *format = json_hash_get(o, "format");
 	if (format != nullptr && format->type == JSON_STRING) {
 		src.format = format->string();
 	}
@@ -3846,7 +3846,7 @@ int main(int argc, char **argv) {
 
 	auto input_ret = read_input(sources, name ? name : out_mbtiles ? out_mbtiles
 								       : out_dir,
-				    maxzoom, minzoom, basezoom, basezoom_marker_width, outdb, out_dir, &exclude, &include, exclude_all, filter, droprate, buffer, tmpdir, gamma, read_parallel, forcetable, attribution, gamma != 0, file_bbox, file_bbox1, file_bbox2, prefilter, postfilter, description, guess_maxzoom, guess_cluster_maxzoom, &attribute_types, argv[0], &attribute_accum, attribute_descriptions, commandline, minimum_maxzoom);
+				    maxzoom, minzoom, basezoom, basezoom_marker_width, outdb, out_dir, &exclude, &include, exclude_all, filter.get(), droprate, buffer, tmpdir, gamma, read_parallel, forcetable, attribution, gamma != 0, file_bbox, file_bbox1, file_bbox2, prefilter, postfilter, description, guess_maxzoom, guess_cluster_maxzoom, &attribute_types, argv[0], &attribute_accum, attribute_descriptions, commandline, minimum_maxzoom);
 
 	ret = std::get<0>(input_ret);