add script to generate fuzz coverage

Author: Prabhat1308

contrib/generate_fuzz_coverage.sh

@@ -0,0 +1,42 @@
+#!/bin/bash
+set -e
+set -x
+
+# Check if we're in the root directory, if so change to fuzz
+if [ -d "fuzz" ]; then
+    cd fuzz
+elif [ ! -f "Cargo.toml" ] || ! grep -q "fuzz" Cargo.toml 2>/dev/null; then
+    echo "Error: Please run this script from the rust-lightning root directory or fuzz directory"
+    exit 1
+fi
+
+# Check if test_cases directory exists and has content
+show_corpus_message=false
+if [ ! -d "test_cases" ]; then
+    show_corpus_message=true
+elif [ -z "$(find test_cases -name '*' -type f 2>/dev/null | head -1)" ]; then
+    show_corpus_message=true
+fi
+
+if [ "$show_corpus_message" = true ]; then
+    echo "Warning: No corpus found in test_cases directory."
+    echo "Generating coverage report without fuzzing corpus."
+    echo ""
+    echo "To include fuzzing corpus coverage, create test_cases directories with your corpus:"
+    echo "  mkdir -p test_cases/{target_name}"
+    echo "  cp your_corpus_directory/* test_cases/{target_name}/"
+    echo ""
+    echo "Example:"
+    echo "  mkdir -p test_cases/base32"
+    echo "  cp /path/to/your/base32_corpus/* test_cases/base32/"
+    echo ""
+fi
+
+export RUSTFLAGS="--cfg=fuzzing --cfg=secp256k1_fuzz --cfg=hashes_fuzz"
+# ignore anything in fuzz directory since we don't want coverage of targets 
+cargo llvm-cov --html --ignore-filename-regex "fuzz/"
+
+echo ""
+echo "Coverage report generated in target/llvm-cov/html/index.html"
+
+