build(test/docs): decouple system WFDB deps and align local build integration
- Disable direct CURL package discovery and linkage in CMake
- Build WFDB with --without-netfiles for local-file focused static integration
- Reduce reliance on system-wide networking dependencies
- Expand README with environment checks, prerequisite installs, and standardized build workflow
- Clarify optional cURL/Expat feature requirements for WFDB components
- Add build/wfdb_install/include to Ceedling include paths
- Enable unit tests to compile against locally provisioned WFDB headers
- Standardize project setup around bundled WFDB artifacts for improved portability and repeatability