Update .gitignore, add chain utils, modify cmake for just main atm

tests/extract_chain.cpp

@@ -0,0 +1,51 @@
+#include <fstream>
+#include <iostream>
+#include <vector>
+#include <cstdint>
+#include <algorithm>
+#include <cstring>
+
+static constexpr uint32_t BLOCK_SIZE = 96 * 1024;
+static constexpr uint32_t NUM_BLOCKS = 4608;
+
+int main(int argc, char* argv[]) {
+    if (argc != 4) {
+        std::cerr << "Usage: " << argv[0] << " <cache_file> <output> <num_blocks>\n";
+        return 1;
+    }
+    
+    std::ifstream cache(argv[1], std::ios::binary);
+    std::ofstream out(argv[2], std::ios::binary);
+    int want_blocks = std::stoi(argv[3]);
+    
+    // Read all slots to find the last written block
+    std::vector<std::pair<int, std::vector<uint8_t>>> slots;
+    std::vector<uint8_t> slot(BLOCK_SIZE);
+    
+    for (int i = 0; i < NUM_BLOCKS; ++i) {
+        cache.read(reinterpret_cast<char*>(slot.data()), BLOCK_SIZE);
+        uint32_t size = *reinterpret_cast<uint32_t*>(slot.data());
+        
+        if (size > 0 && size < BLOCK_SIZE - 4) {
+            std::vector<uint8_t> data(size);
+            memcpy(data.data(), slot.data() + 4, size);
+            slots.push_back({i, std::move(data)});
+        }
+    }
+    
+    std::cout << "Found " << slots.size() << " valid blocks in cache\n";
+    
+    // Take the last N blocks (most recent)
+    int start = std::max(0, (int)slots.size() - want_blocks);
+    int written = 0;
+    
+    for (int i = start; i < slots.size(); ++i) {
+        uint32_t size = slots[i].second.size();
+        out.write(reinterpret_cast<char*>(&size), 4);
+        out.write(reinterpret_cast<char*>(slots[i].second.data()), size);
+        written++;
+    }
+    
+    std::cout << "Extracted " << written << " consecutive blocks (slots " << slots[start].first << " to " << slots.back().first << ")\n";
+    return 0;
+}