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/cbindgen.toml

@@ -0,0 +1,23 @@
+[parse]
+parse_deps = false
+include = []
+
+[export]
+include = ["EntropykErrorCode", "EntropykConvergenceStatus", "EntropykSystem", "EntropykComponent", "EntropykSolverResult", "EntropykNewtonConfig", "EntropykPicardConfig", "EntropykFallbackConfig"]
+
+[fn]
+sort_by = "Name"
+
+[struct]
+rename_fields = "None"
+
+[enum]
+rename_variants = "ScreamingSnakeCase"
+
+[macro_expansion]
+bitflags = true
+
+[defines]
+"target_os = linux" = "ENTROPYK_LINUX"
+"target_os = macos" = "ENTROPYK_MACOS"
+"target_os = windows" = "ENTROPYK_WINDOWS"