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

CHANGELOG.md

@@ -1,5 +1,13 @@
 # 2.81.0
 
+* Report errors from the tile clipping and overzooming code by throwing a
+  `tippecanoe_error` rather than by calling `exit()`, and give that code
+  RAII ownership of its `FILE *` and `json_pull *` handles so that nothing
+  leaks when an error unwinds the stack. Each command-line tool catches the
+  exception in `main()` and exits with the same status it would have
+  before. Along the way this fixes a leaked `z_stream` when `compress()`
+  failed and two `exit()` calls that could run from a destructor or from
+  `mvt_value`'s hash function.
 * Add `--drop-by-attribute-as-needed=`*attribute* to drop the features with
   the lowest values of a numeric attribute from oversized tiles, and
   `--drop-by-attribute-order=desc` to drop the highest values instead.