feat(rate-limiting): Implement core rate limiting functionality with configuration, decision-making, metrics, middleware, and service registration

- Add RateLimitConfig for configuration management with YAML binding support.
- Introduce RateLimitDecision to encapsulate the result of rate limit checks.
- Implement RateLimitMetrics for OpenTelemetry metrics tracking.
- Create RateLimitMiddleware for enforcing rate limits on incoming requests.
- Develop RateLimitService to orchestrate instance and environment rate limit checks.
- Add RateLimitServiceCollectionExtensions for dependency injection registration.

datasets/reachability/ground-truth/unreachable/gt-0012/main.c

@@ -0,0 +1,28 @@
+// gt-0012: Compile-time constant false condition
+// Expected: UNREACHABLE (tier: imported)
+// Vulnerability: CWE-120 (Buffer Overflow)
+
+#include <stdio.h>
+#include <string.h>
+
+#define DEBUG_MODE 0  // Compile-time constant
+
+int main(int argc, char *argv[]) {
+    char buffer[64];
+    
+    // This branch is constant false - will be optimized out
+    if (DEBUG_MODE) {
+        // Vulnerable code in dead branch
+        gets(buffer);  // SINK: CWE-120 (but unreachable)
+        printf("Debug: %s\n", buffer);
+    } else {
+        // Safe path always taken
+        if (argc > 1) {
+            strncpy(buffer, argv[1], sizeof(buffer) - 1);
+            buffer[sizeof(buffer) - 1] = '\0';
+            printf("Input: %s\n", buffer);
+        }
+    }
+    
+    return 0;
+}