[SYSTEMDS-3891] OOC Source Streams

[janniklinde]

This patch introduces a new SourceStream which is produced by OOCReblockInstruction. This change aims to prevent redundant disk writes caused by CachingStreams evicting the direct output of an upstream reblock instruction. The SourceStream triggers custom cache handling in the CachingStream and maintains an index for future direct access of source tiles on disk.

These changes lead to significant speedups, allowing us to perform PCA on a 1Mx1000 input matrix in ~26s compared to the previous ~40s on our local machine (although some of the observed speedups came from the now parallel read in OOCReblockInstruction which was previously not possible due to OOM errors for 5GB of allowed RAM).
In addition, we are now able to run the same PCA script with 1GB of memory, which completes in ~31s.

5GB:

1GB:

Experiments on the scale-out node also show significant speedups of PCA, reaching a 3x speedup over CP.

mode	conf	run [s]
cp	100g	33.061
ooc	100g	10.502
cp	10g	nan
ooc	10g	13.767
cp	1g	nan
ooc	1g	19.031

[mboehm7]

LGTM - thanks for the improvement @janniklinde. The performance numbers under different JVM sizes are already very promising. Great job.