feat: add bytes.indexOf, server.acceptBatch, server.pendingCount, stdin data callback, and coverage/valgrind make targets

Implement `bytesIndexOf` foreign function supporting optional start offset for searching byte sequences. Add `serverAcceptBatch` and `serverPendingCount` to net module for batch accepting connections and querying pending queue size. Refactor `stdinFileTimerCallback` to pass read bytes to Wren callback instead of null, with separate handling for EOF. Introduce `coverage_64bit` build config with gcov flags, plus `coverage`, `valgrind`, `clean-coverage`, and `publish` phony targets in Makefile. Fix memory leak in regex by nullifying freed pointers on allocation failure.

Makefile

@@ -1,6 +1,6 @@
 # retoor <retoor@molodetz.nl>
 
-.PHONY: build tests clean debug sync-sidebar buildmanual wasm wasm-clean install-emscripten
+.PHONY: build tests clean debug sync-sidebar buildmanual wasm wasm-clean install-emscripten coverage valgrind clean-coverage
 
 build:
 	cd projects/make && $(MAKE) -f wren_cli.make -j $$(nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 4)
@@ -26,6 +26,14 @@ install:
 clean:
 	cd projects/make && $(MAKE) -f wren_cli.make clean
 
+publish:
+	git add src
+	git add example
+	git add manual_src
+	git add test
+	git commit -a -m "Update."
+	git push
+
 wasm-clean:
 	cd projects/make.wasm && $(MAKE) -f wren_wasm.make clean
 
@@ -50,3 +58,22 @@ wasm:
 
 buildmanual:
 	python3 util/build_manual.py
+
+coverage:
+	cd projects/make && $(MAKE) -f wren_cli.make config=coverage_64bit clean
+	cd projects/make && $(MAKE) -f wren_cli.make config=coverage_64bit -j $$(nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 4)
+	python3 util/test.py --suffix=_cov
+	@echo "Generating coverage report..."
+	lcov --capture --directory projects/make/obj/64bit/Coverage --output-file coverage.info --ignore-errors mismatch,inconsistent
+	lcov --remove coverage.info '/usr/*' '*/deps/*' --output-file coverage.info --ignore-errors unused
+	genhtml coverage.info --output-directory coverage_report
+	@echo "Coverage report: coverage_report/index.html"
+
+valgrind:
+	cd projects/make && $(MAKE) -f wren_cli.make config=debug_64bit -j $$(nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 4)
+	python3 util/test.py --suffix=_d --valgrind
+
+clean-coverage:
+	rm -rf coverage.info coverage_report
+	find projects/make -name "*.gcda" -delete
+	find projects/make -name "*.gcno" -delete