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/box/hak_free_api.inc.h

@@ -12,6 +12,7 @@
 #endif
 
 // Optional route trace: print first N classification lines when enabled by env
+#if !HAKMEM_BUILD_RELEASE
 static inline int hak_free_route_trace_on(void) {
     static int g_trace = -1;
     if (__builtin_expect(g_trace == -1, 0)) {
@@ -31,6 +32,9 @@ static inline void hak_free_route_log(const char* tag, void* p) {
     (*budget)--;
     fprintf(stderr, "[FREE_ROUTE] %s ptr=%p\n", tag, p);
 }
+#else
+static inline void hak_free_route_log(const char* tag, void* p) { (void)tag; (void)p; }
+#endif
 
 // Optional: request-trace for invalid-magic cases (first N hits)
 static inline int hak_super_reg_reqtrace_on(void) {
@@ -74,6 +78,7 @@ void hak_free_at(void* ptr, size_t size, hak_callsite_t site) {
 #endif
     (void)site; (void)size;
     // Optional lightweight trace of early free calls (first few only)
+#if !HAKMEM_BUILD_RELEASE
     static int free_trace_en = -1; static _Atomic int free_trace_count = 0;
     if (__builtin_expect(free_trace_en == -1, 0)) {
         const char* e = getenv("HAKMEM_FREE_WRAP_TRACE");
@@ -85,6 +90,7 @@ void hak_free_at(void* ptr, size_t size, hak_callsite_t site) {
             fprintf(stderr, "[FREE_WRAP_ENTER] ptr=%p\n", ptr);
         }
     }
+#endif
     if (!ptr) {
 #if HAKMEM_DEBUG_TIMING
         HKM_TIME_END(HKM_CAT_HAK_FREE, t0);