Support editable mode

[vineetbansal]

scikit-build-core doesn't seem to be installing the iphreeqc_database component when installing in editable mode:

set(IPHREEQC_DATABASE_DIR   ${IPHREEQC_BASE}/database)
install(DIRECTORY
      "${IPHREEQC_DATABASE_DIR}"
      DESTINATION pyphreeqc COMPONENT iphreeqc_database)

Probably the install targets have to be defined explicitly in pyproject.toml?