fuzz: fix coverage report to include library crates

Since cargo-llvm-cov 0.7.0, only workspace members are instrumented
by default. Since the fuzz crate is a standalone workspace, library
crates like lightning were not instrumented, and the coverage report
was empty.

Add --dep-coverage to instrument the library path dependencies.

This alone is not sufficient for the report: --dep-coverage's report
filtering only supports crates.io deps, not path deps (per a TODO in
cargo-llvm-cov source). Add --no-default-ignore-filename-regex to
include all instrumented code, then use a custom --ignore-filename-regex
to exclude unwanted paths (cargo registry, rustup toolchains, fuzz
harness).

AI tools were used in preparing this commit.

Author: joostjager

contrib/generate_fuzz_coverage.sh

@@ -57,7 +57,11 @@ mkdir -p "$OUTPUT_DIR"
 
 # dont run this command when running in CI
 if [ "$OUTPUT_CODECOV_JSON" = "0" ]; then
-    cargo llvm-cov --html --ignore-filename-regex "fuzz/" --output-dir "$OUTPUT_DIR"
+    cargo llvm-cov --html \
+        --dep-coverage lightning,lightning-invoice,lightning-liquidity,lightning-rapid-gossip-sync,lightning-persister \
+        --no-default-ignore-filename-regex \
+        --ignore-filename-regex "(\.cargo/registry|\.rustup/toolchains|/fuzz/)" \
+        --output-dir "$OUTPUT_DIR"
     echo "Coverage report generated in $OUTPUT_DIR/html/index.html"
 else
     # Clean previous coverage artifacts to ensure a fresh run.
@@ -78,7 +82,10 @@ else
     fi
 
     echo "Replaying imported corpus (if found) via tests to generate coverage..."
-    cargo llvm-cov -j8 --codecov --ignore-filename-regex "fuzz/" \
+    cargo llvm-cov -j8 --codecov \
+        --dep-coverage lightning,lightning-invoice,lightning-liquidity,lightning-rapid-gossip-sync,lightning-persister \
+        --no-default-ignore-filename-regex \
+        --ignore-filename-regex "(\.cargo/registry|\.rustup/toolchains|/fuzz/)" \
         --output-path "$OUTPUT_DIR/fuzz-codecov.json" --tests
 
     echo "Fuzz codecov report available at $OUTPUT_DIR/fuzz-codecov.json"