Add physics, heap, json_helpers, game, and actor test suites

Raise line coverage from 39.6 to 61.8 percent with four new suites and an
extension to the actor suite, and register every suite through a single
CMake list so a new test file cannot be left out of the coverage fixture.
Give the test targets a build-tree RPATH and prepend the build tree to
LD_LIBRARY_PATH for CTest, so a developer with a previously installed
libakgl.so exercises the library that was just compiled.

Fix six defects the new tests exposed:

- akgl_physics_simulate read self->gravity_time before its NULL check, so a
  NULL backend crashed instead of reporting AKERR_NULLPOINTER.
- akgl_game_save transposed CLEANUP and PROCESS, which placed the fclose
  inside the PROCESS switch. An ordinary save never flushed or closed its
  stream and produced an empty file.
- akgl_game_save_actors wrote each name table terminator from the address of
  a single char, emitting stack contents into the save file and a sentinel
  the loader could not recognize.
- akgl_game_load_objectnamemap used CATCH directly inside while(1), where the
  break leaves the loop rather than propagating, so a truncated name table
  loaded as a successful game.
- akgl_Actor_cmhf_up_on and _down_on dereferenced actor->basechar with no
  NULL check, unlike their left and right counterparts.
- akgl_actor_logic_movement checked actor twice instead of checking
  actor->basechar before dereferencing it.

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

tests/testutil.h

@@ -0,0 +1,99 @@
+/**
+ * @file testutil.h
+ * @brief Shared assertion helpers and headless bootstrap for the libakgl test suites.
+ *
+ * The akerror ATTEMPT/CATCH/PROCESS/FINISH macros are verbose when what a test
+ * wants to say is "this call must fail with exactly this status". These helpers
+ * wrap that pattern.
+ *
+ * All of the TEST_* assertion macros expand to a `break` on failure, so they
+ * must be used directly inside an ATTEMPT block. Inside a `for` or `while`
+ * nested in an ATTEMPT they would break the inner loop instead; use
+ * TEST_ASSERT_FLAG in that case and check the flag after the loop.
+ */
+
+#ifndef _AKGL_TESTUTIL_H_
+#define _AKGL_TESTUTIL_H_
+
+#include <math.h>
+#include <SDL3/SDL.h>
+#include <akerror.h>
+#include <akgl/error.h>
+
+/** @brief Fail the enclosing ATTEMPT block unless @p cond holds. */
+#define TEST_ASSERT(e, cond, ...)					\
+    if ( ! (cond) ) {							\
+	FAIL_BREAK(e, AKGL_ERR_BEHAVIOR, __VA_ARGS__);			\
+    }
+
+/**
+ * @brief Run @p stmt and require that it reports exactly @p expected.
+ *
+ * Releases whatever context @p stmt returns, so a test can assert many failure
+ * paths in a row without draining AKERR_ARRAY_ERROR. Pass 0 for @p expected to
+ * require success.
+ */
+#define TEST_EXPECT_STATUS(e, expected, stmt, desc)			\
+    {									\
+	akerr_ErrorContext *__tec = (stmt);				\
+	int __tst = ( __tec == NULL ) ? 0 : __tec->status;		\
+	if ( __tec != NULL ) {						\
+	    __tec->handled = true;					\
+	    __tec = akerr_release_error(__tec);				\
+	}								\
+	if ( __tst != (expected) ) {					\
+	    FAIL_BREAK(							\
+		e,							\
+		AKGL_ERR_BEHAVIOR,					\
+		"%s: expected status %d (%s), got %d (%s)",		\
+		desc,							\
+		(int)(expected),					\
+		akerr_name_for_status((int)(expected), NULL),		\
+		__tst,							\
+		akerr_name_for_status(__tst, NULL));			\
+	}								\
+    }
+
+/** @brief Require that @p stmt succeeds, reporting @p desc if it does not. */
+#define TEST_EXPECT_OK(e, stmt, desc)		\
+    TEST_EXPECT_STATUS(e, 0, stmt, desc)
+
+/**
+ * @brief Require that @p stmt fails, without pinning which status it reports.
+ *
+ * For paths that are delegated to a dependency, where the exact status is that
+ * dependency's business and asserting it would make the test brittle.
+ */
+#define TEST_EXPECT_ANY_ERROR(e, stmt, desc)				\
+    {									\
+	akerr_ErrorContext *__tec = (stmt);				\
+	int __tst = ( __tec == NULL ) ? 0 : __tec->status;		\
+	if ( __tec != NULL ) {						\
+	    __tec->handled = true;					\
+	    __tec = akerr_release_error(__tec);				\
+	}								\
+	if ( __tst == 0 ) {						\
+	    FAIL_BREAK(e, AKGL_ERR_BEHAVIOR, "%s: expected a failure, got success", desc); \
+	}								\
+    }
+
+/** @brief Require that two floats agree to within AKGL_TEST_EPSILON. */
+#define AKGL_TEST_EPSILON 0.0001f
+
+#define TEST_ASSERT_FEQ(e, actual, expected, ...)			\
+    if ( fabsf((float)(actual) - (float)(expected)) > AKGL_TEST_EPSILON ) { \
+	FAIL_BREAK(e, AKGL_ERR_BEHAVIOR, __VA_ARGS__);			\
+    }
+
+/**
+ * @brief Record a failure into a flag instead of breaking.
+ *
+ * For assertions inside a loop nested in an ATTEMPT block, where `break` would
+ * only leave the loop.
+ */
+#define TEST_ASSERT_FLAG(flag, cond)		\
+    if ( ! (cond) ) {				\
+	(flag) = false;				\
+    }
+
+#endif // _AKGL_TESTUTIL_H_