feat: implement mass balance validation for Story 7.1

- Added port_mass_flows to Component trait and implements for core components.
- Added System::check_mass_balance and integrated it into the solver.
- Restored connect methods for ExpansionValve, Compressor, and Pipe to fix integration tests.
- Updated Python and C bindings for validation errors.
- Updated sprint status and story documentation.

bindings/c/tests/Makefile

@@ -0,0 +1,45 @@
+CC ?= gcc
+CFLAGS = -Wall -Wextra -O2 -I../../../target
+
+UNAME_S := $(shell uname -s)
+ifeq ($(UNAME_S),Darwin)
+    LIB_EXT = dylib
+    LDFLAGS = -L../../../target/release -lentropyk_ffi
+else ifeq ($(UNAME_S),Linux)
+    LIB_EXT = so
+    LDFLAGS = -L../../../target/release -lentropyk_ffi -Wl,-rpath,'$$ORIGIN/../../../target/release'
+else
+    LIB_EXT = dll
+    LDFLAGS = -L../../../target/release -lentropyk_ffi
+endif
+
+TESTS = test_lifecycle test_errors test_solve test_latency test_memory
+
+.PHONY: all clean run valgrind
+
+all: $(TESTS)
+
+$(TESTS): %: %.c ../../../target/entropyk.h ../../../target/release/libentropyk_ffi.$(LIB_EXT)
+	$(CC) $(CFLAGS) -o $@ $< $(LDFLAGS)
+
+../../../target/entropyk.h ../../../target/release/libentropyk_ffi.$(LIB_EXT):
+	cd ../../.. && cargo build --release -p entropyk-c
+
+run: $(TESTS)
+	@echo "Running all tests..."
+	@for test in $(TESTS); do \
+		echo "\n=== $$test ==="; \
+		./$$test || exit 1; \
+	done
+	@echo "\nAll tests PASSED"
+
+valgrind: $(TESTS)
+	@echo "Running valgrind memory checks..."
+	@for test in $(TESTS); do \
+		echo "\n=== $$test (valgrind) ==="; \
+		valgrind --leak-check=full --error-exitcode=1 ./$$test || exit 1; \
+	done
+	@echo "\nAll valgrind checks PASSED"
+
+clean:
+	rm -f $(TESTS)