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-0011/main.c

@@ -0,0 +1,25 @@
+// gt-0011: Dead code - function never called
+// Expected: UNREACHABLE (tier: imported)
+// Vulnerability: CWE-120 (Buffer Copy without Checking Size)
+
+#include <stdio.h>
+#include <string.h>
+
+// This function is NEVER called - dead code
+void vulnerable_function(const char *input) {
+    char buffer[32];
+    strcpy(buffer, input);  // SINK: CWE-120 (but unreachable)
+    printf("Value: %s\n", buffer);
+}
+
+void safe_function(const char *input) {
+    printf("Safe: %.31s\n", input);
+}
+
+int main(int argc, char *argv[]) {
+    if (argc > 1) {
+        // Only safe_function is called
+        safe_function(argv[1]);
+    }
+    return 0;
+}

datasets/reachability/ground-truth/unreachable/gt-0011/sample.manifest.json

@@ -0,0 +1,27 @@
+{
+  "$schema": "https://stellaops.io/schemas/sample-manifest.v1.json",
+  "sampleId": "gt-0011",
+  "version": "1.0.0",
+  "category": "unreachable",
+  "description": "Dead code - function never called - UNREACHABLE",
+  "language": "c",
+  "expectedResult": {
+    "reachable": false,
+    "tier": "imported",
+    "confidence": 1.0
+  },
+  "source": {
+    "files": ["main.c"],
+    "entrypoint": "main",
+    "sink": "strcpy",
+    "vulnerability": "CWE-120"
+  },
+  "callChain": null,
+  "annotations": {
+    "notes": "Vulnerable function exists but is never called from any reachable path",
+    "difficulty": "trivial",
+    "reason": "dead_code"
+  },
+  "createdAt": "2025-12-17T00:00:00Z",
+  "createdBy": "corpus-team"
+}