Rename wfdb_process library target and DATASET_DIR, gate lib_demo build
- Rename "wfdb_process" target to "wfdb_process-lib"
- Gate demo executable behind new LIB_DEMO_ENABLE option (default OFF)
- Rename DATASET_DIR to WFDB_PROCESS_DATASET_DIR to avoid collisions
- Remove redundant enable_language(C CXX), -O2 flags
- Update CI, README, and project.yml.in for the above renames