Fix CI test segfault: clamp stack ulimit before odin test

Root cause found via gdb backtrace on the runner (thread::pool_init
crashed from main -> testing runner): the CI container sets
`ulimit -s unlimited`, so getrlimit(RLIMIT_STACK) returns RLIM_INFINITY.
core:thread passes that to pthread_attr_setstacksize, pthread_create
fails, and thread.create() returns nil, which core:testing's pool_init
dereferences without a nil check. Reproduced and confirmed fixed in an
ubuntu:24.04 container with the same Odin build. `just test` now clamps
the stack limit before running odin test. Also removes the gdb
diagnostic step added to debug this.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

justfile

@@ -28,6 +28,11 @@ check:
 # Run the test suite (single-threaded: the tests share the memory game's global state)
 test:
     mkdir -p {{build_dir}}
+    # If the stack rlimit is "unlimited" (RLIM_INFINITY, as some CI/container hosts set it),
+    # Odin's core:thread passes that straight to pthread_attr_setstacksize, pthread_create
+    # then fails, and thread.create() returns nil - which core:testing's pool_init
+    # dereferences unconditionally, segfaulting the whole test binary. Clamp it.
+    ulimit -s 8192
     odin test tests -vet -define:ODIN_TEST_THREADS=1 -out:{{build_dir}}/tests
 
 # Optimized native build into build/<os>/, with the assets it needs at runtime