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-0013/main.c

@@ -0,0 +1,27 @@
+// gt-0013: Ifdef-excluded code path
+// Expected: UNREACHABLE (tier: imported)
+// Vulnerability: CWE-78 (OS Command Injection)
+// Compile with: gcc -DPRODUCTION main.c (LEGACY_SHELL not defined)
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define PRODUCTION
+
+void process_command(const char *cmd) {
+#ifdef LEGACY_SHELL
+    // This code is excluded when LEGACY_SHELL is not defined
+    system(cmd);  // SINK: CWE-78 (but unreachable - ifdef excluded)
+#else
+    // Safe path: just print, don't execute
+    printf("Would execute: %s\n", cmd);
+#endif
+}
+
+int main(int argc, char *argv[]) {
+    if (argc > 1) {
+        process_command(argv[1]);
+    }
+    return 0;
+}

datasets/reachability/ground-truth/unreachable/gt-0013/sample.manifest.json

@@ -0,0 +1,27 @@
+{
+  "$schema": "https://stellaops.io/schemas/sample-manifest.v1.json",
+  "sampleId": "gt-0013",
+  "version": "1.0.0",
+  "category": "unreachable",
+  "description": "Ifdef-excluded code path - UNREACHABLE",
+  "language": "c",
+  "expectedResult": {
+    "reachable": false,
+    "tier": "imported",
+    "confidence": 1.0
+  },
+  "source": {
+    "files": ["main.c"],
+    "entrypoint": "main",
+    "sink": "system",
+    "vulnerability": "CWE-78"
+  },
+  "callChain": null,
+  "annotations": {
+    "notes": "Vulnerable code excluded by preprocessor directive",
+    "difficulty": "easy",
+    "reason": "preprocessor_excluded"
+  },
+  "createdAt": "2025-12-17T00:00:00Z",
+  "createdBy": "corpus-team"
+}