feat(real-world-vfc-slice): add labeled OpenSSL/Firefox/Chromium/curl pair corpus

Harvest 176 isolated vuln-vs-fix functions (109 CVEs, 352 training rows)
into benchmarks/pairs/vfc with provenance and a JSONL training manifest.
Score the slice as an honesty dashboard (ousast pairs --slice vfc);
keep the pair gate on the local fixtures only.

benchmarks/pairs/vfc/openssl-cve-2021-3712-ia5ncasecmp/fixed.c

@@ -0,0 +1,36 @@
+/* Provenance: openssl/openssl ia5ncasecmp (fixed).
+ * repo: openssl/openssl
+ * commit: d2015a783e64613d8e4a142fa05048d1863df944
+ * parent: 918430ba80d94ec8f05383b43b1872b1ebb13e1a
+ * commit_url: https://github.com/openssl/openssl/commit/d2015a783e64613d8e4a142fa05048d1863df944
+ * cve: CVE-2021-3712
+ * license: OpenSSL License
+ * function: ia5ncasecmp
+ * relpath: crypto/x509/v3_ncons.c
+ */
+
+static int ia5ncasecmp(const char *s1, const char *s2, size_t n)
+{
+    for (; n > 0; n--, s1++, s2++) {
+        if (*s1 != *s2) {
+            unsigned char c1 = (unsigned char)*s1, c2 = (unsigned char)*s2;
+
+            /* Convert to lower case */
+            if (c1 >= 0x41 /* A */ && c1 <= 0x5A /* Z */)
+                c1 += 0x20;
+            if (c2 >= 0x41 /* A */ && c2 <= 0x5A /* Z */)
+                c2 += 0x20;
+
+            if (c1 == c2)
+                continue;
+
+            if (c1 < c2)
+                return -1;
+
+            /* c1 > c2 */
+            return 1;
+        }
+    }
+
+    return 0;
+}