Fix every memory defect the checker found, and bump to 0.4.0

Six findings, all of them libakgl's, all closed. The memcheck run is clean.

Not one of the four json_load_file calls in src/ was ever matched by a
json_decref, so every asset load abandoned its parsed document: 1.5 KB per
sprite, 2.1 KB per character, 9 KB per load of the 2x2 fixture map, and on
the order of a megabyte for a real one. Each loader now releases it in the
CLEANUP block it already had, on the success path as well as the failure
one. akgl_registry_load_properties needed its loop moved inside the ATTEMPT
block first: props is a borrowed reference into the document and is read
after the block ends, so every exit from that loop leaked the whole tree.

akgl_get_property copied a fixed AKGL_MAX_STRING_LENGTH bytes out of what
SDL handed back, which is SDL's strdup of the value -- four bytes for
"0.0". That read up to 4 KiB past the end of somebody else's allocation on
every property read, returned whatever was there past the terminator, and
would have faulted on a value that landed at the end of a page. It copies
the value and its terminator now, and refuses a value too long for an
akgl_String rather than truncating it into an unterminated buffer. The
header note that described the overread as a quirk describes correct
behaviour instead.

The four savegame name tables wrote a fixed-width field starting at the
registry key, and SDL sizes that allocation to the name. They read past it
on every entry and put what they found into the save file: up to half a
kilobyte of this process's heap per registered object, in a file a player
might send to somebody. They stage through a zeroed buffer now, and a
negative-array-size typedef fails the build if a table's width ever outgrows
it.

akgl_controller_list_keyboards never freed the array SDL_GetKeyboards
allocated for it.

A font could be opened and published and never handed back -- there was no
way to close one, so a game that changed fonts between scenes leaked ten
kilobytes each time, and loading over a live name leaked the font it
displaced. akgl_text_unloadfont is that missing half, and akgl_text_loadfont
calls it when it replaces a name, after the new font has opened so a failed
reload leaves the caller with the font they had. A new public symbol takes
the version to 0.4.0 and the soname with it: an 0.3 consumer cannot be
handed this library and told it is the same ABI.

tests/registry.c fills a destination with a sentinel and asserts the bytes
past the terminator survive a read, which fails against the old copy.
tests/text.c covers unload, double unload, unloading a name that was never
registered, and replacement closing the displaced font. The JSON releases
have no test of their own and cannot sensibly have one -- nothing in the
public API can observe a jansson refcount -- so the memcheck run is their
test, which is an argument for gating it rather than against.

The two remaining findings are in deps/semver's own unit test, which is
vendored. They are suppressed by function name, so a rewrite of those cases
comes back as a finding.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

include/akgl/text.h

@@ -29,7 +29,9 @@
  *
  * @param name     Registry key to publish the font under. Required. An existing
  *                 entry with the same name is replaced, and the font it
- *                 displaced is leaked rather than closed.
+ *                 displaced is closed through akgl_text_unloadfont -- but only
+ *                 after the new one has opened, so a failed load leaves the
+ *                 caller with the font they already had.
  * @param filepath Path to a `.ttf`/`.otf` file. Required. Used verbatim -- not
  *                 resolved against `SDL_GetBasePath()`.
  * @param size     Point size to rasterize at. Passed straight to SDL_ttf, which
@@ -43,6 +45,30 @@
  *         in practice, because akgl_registry_init has not run.
  */
 akerr_ErrorContext AKERR_NOIGNORE *akgl_text_loadfont(char *name, char *filepath, int size);
+/**
+ * @brief Close a loaded font and take it out of the font registry.
+ *
+ * The other half of akgl_text_loadfont, and for a while the half that did not
+ * exist: a font could be opened and published but never handed back, so a game
+ * that changed fonts between scenes had no way to reclaim the one it had
+ * finished with. A `TTF_Font` is about ten kilobytes once FreeType's own
+ * structures are counted.
+ *
+ * The registry entry is cleared before the font is closed, so a font is never
+ * reachable through #AKGL_REGISTRY_FONT after it has gone back to SDL_ttf.
+ *
+ * @param name Registry key the font was published under. Required.
+ * @return `NULL` on success, otherwise an error context owned by the caller.
+ * @throws AKERR_NULLPOINTER If @p name is `NULL`.
+ * @throws AKERR_KEY If no font is registered under @p name -- including the
+ *         case where it was already unloaded, which makes a double unload an
+ *         error rather than a double close.
+ *
+ * @warning Anything still holding the `TTF_Font *` -- a caller that fetched it
+ *          from the registry earlier, a pending akgl_text_rendertextat -- is
+ *          left with a dangling pointer. Fonts are not reference counted.
+ */
+akerr_ErrorContext AKERR_NOIGNORE *akgl_text_unloadfont(char *name);
 /**
  * @brief Rasterize a string and blit it at a screen position, in one call.
  *