Fix critical memory safety issues

[jserv]

This adds explicit NULL checks for all malloc/calloc/mpool_alloc calls that previously relied solely on assert(), which compiles out with -DNDEBUG. It prevents NULL pointer dereferences in production builds.

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Summary by cubic

Adds NULL checks and graceful fallbacks for critical allocations across the emulator, JIT, cache, IO, and syscalls. Prevents crashes when assert() is disabled and degrades behavior safely on OOM.

• Bug Fixes
  • Block/IR/branch-table allocations now checked; translation can fail cleanly.
  • Fused operation generation falls back to non-fused ops if malloc fails.
  • JIT init and queue entry allocations validated; cleanup on failure; skip tier-2 enqueue on OOM.
  • Cache put restores the replaced entry if new allocation fails.
  • IO, syscall, and riscv init guard malloc/calloc; return NULL or -1 instead of crashing.

[jserv]

Benchmarks

Benchmark suite	Current: adab7d7	Previous: 9220ffb	Ratio
Dhrystone	1302 Average DMIPS over 10 runs	1267 Average DMIPS over 10 runs	0.97
Coremark	952.843 Average iterations/sec over 10 runs	958.558 Average iterations/sec over 10 runs	1.01

This comment was automatically generated by workflow using github-action-benchmark.

[visitorckw]

Perhaps we can consider introducing a fault injection framework down the road to improve test coverage for error handling cases such as this one.