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/examples/Makefile

@@ -0,0 +1,31 @@
+CC ?= gcc
+CFLAGS = -Wall -Wextra -O2 -I../../../target
+
+# Platform-specific library extension
+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
+
+.PHONY: all clean run
+
+all: example
+
+example: example.c ../../../target/entropyk.h ../../../target/release/libentropyk.$(LIB_EXT)
+	$(CC) $(CFLAGS) -o $@ $< $(LDFLAGS)
+
+../../../target/entropyk.h ../../../target/release/libentropyk.$(LIB_EXT):
+	cd ../../.. && cargo build --release -p entropyk-c
+
+run: example
+	./example
+
+clean:
+	rm -f example