cdc: reduce dependencies on captured variables in process_cells
cdc: reduce dependencies on captured variables in process_cells

This is a preparation for moving the lambda outside the for loop.

- `log_ck`, `pikey`, `pirow` are now passed as arguments,
- `value` is now a variable local to the lambda,
- `ttl` is now a variable local to the lambda that is returned.

avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla