Optimizing Remote Table Reads with Smaller Tasks and 1MB Buffers

For reading from remote tables we use smaller tasks (instead of reading the whole part) to make tasks stealing work * task size is determined by size of columns to read * always use 1mb buffers for reading from s3 * boundaries of cache segments aligned to 1mb so they have decent size even with small tasks. it also should prevent fragmentation. #49287 (Nikita Taranov).