Rename nibp_algorithm target to nibp_algorithm-lib, use FetchDependencies, gate demo executable
- Rename library target from "nibp_algorithm" to "nibp_algorithm-lib"
- Replace manual FetchContent blocks for averaging, c_helpers, wfdb_process, csv_process, and filtering with FetchDependencies module
- Add LIB_DEMO_ENABLE option (default OFF) to gate the demo executable
- Drop -Wall -Wextra -Werror and redundant enable_language(C CXX)
- Update project.yml.in
- Document LIB_DEMO_ENABLE in README and update doc-generation command
- Add "*.csv" to .gitignore