Remove debug overhead from release builds (19 hotspots)

Problem:
- Release builds (-DHAKMEM_BUILD_RELEASE=1) still execute debug code
- fprintf, getenv(), atomic counters in hot paths
- Performance: 9M ops/s vs System malloc 43M ops/s (4.8x slower)

Fixed hotspots:
1. hak_alloc_api.inc.h - atomic_fetch_add + fprintf every alloc
2. hak_free_api.inc.h - Free wrapper trace + route trace
3. hak_wrappers.inc.h - Malloc wrapper logs
4. tiny_free_fast.inc.h - getenv() every free (CRITICAL!)
5. hakmem_tiny_refill.inc.h - Expensive validation
6. hakmem_tiny_sfc.c - SFC initialization logs
7. tiny_alloc_fast_sfc.inc.h - getenv() caching

Changes:
- Guard all fprintf/printf with #if !HAKMEM_BUILD_RELEASE
- Cache getenv() results in TLS variables (debug builds only)
- Remove atomic counters from hot paths in release builds
- Add no-op stubs for release builds

Impact:
- All debug code completely eliminated in release builds
- Expected improvement: Limited (deeper profiling needed)
- Root cause: Performance bottleneck exists beyond debug overhead

Note: Benchmark results show debug removal alone insufficient for
performance goals. Further investigation required with perf profiling.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

core/tiny_alloc_fast_sfc.inc.h

@@ -108,8 +108,12 @@ static inline int sfc_free_push(int cls, void* ptr) {
 #if !HAKMEM_BUILD_RELEASE && defined(HAKMEM_SFC_DEBUG_LOG)
     // Debug logging (compile-time gated; zero cost in release)
     do {
+        static __thread int free_debug_enabled = -1;
         static __thread int free_debug_count = 0;
-        if (getenv("HAKMEM_SFC_DEBUG") && free_debug_count < 20) {
+        if (__builtin_expect(free_debug_enabled == -1, 0)) {
+            free_debug_enabled = getenv("HAKMEM_SFC_DEBUG") ? 1 : 0;
+        }
+        if (free_debug_enabled && free_debug_count < 20) {
             free_debug_count++;
             extern int g_sfc_enabled;
             fprintf(stderr, "[SFC_FREE_PUSH] cls=%d, ptr=%p, cnt=%u, cap=%u, will_succeed=%d, enabled=%d\n",