qa/standalone: osd-scrub-dump.sh: additional tests

Also - adding stride override parameter to the existing
large-object scrub test. And: improving the output format
of the test results.

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>

osd/scrub: extract the 'read object data' functionality

from be_deep_scrub() into a separate function,
ReplicatedBackend::be_deep_scrub_read().

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>

osd/scrub: do not attempt to read past the end of an object

When performing deep scrubs, the scrubber reads object data
in strides. Existing code uses a short read to detect the end
of the object (and if the object size is a multiple of the
stride - an extra read is performed, which returns 0 bytes).

The proposed change is to avoid such extra read attempts,
by using our knowledge of the object size.

Also - some minor code cleanups in the relevant function.

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>

osd: provide fmtlib formatter for ScrubMapBuilder

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>

Merge pull request #66230 from ronen-fr/wip-rf-larger-stride

osd/scrub: increasing the default data-read stride

Reviewed-by: Radoslaw Zarzynski <rzarzyns@redhat.com>
Reviewed-by: Anthony D'Atri <anthony.datri@gmail.com>
Reviewed-by: Alex Ainscow <aainscow@uk.ibm.com>
Reviewed-by: Jon Bailey <jonathan.bailey1@ibm.com>

Merge pull request #64248 from zhuwei127/fix-doublefree

examples/librados: fix memory pointed to by 'rs' is freed twice.

Reviewed-by: Patrick Donnelly <pdonnell@ibm.com>

common/options: document osd_deep_scrub_stride

default value change (from 0.5MB to 4MB)

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>

qa/standalone: osd-scrub-dump.sh: test large object scrubs

following a change to the default stride size for deep scrubs,
adding a standalone test to verify that scrubs of large objects
work correctly (and to perform some minimal performance
measurements).

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>

osd/scrub: increasing the default data-read stride

When performing deep scrubs, the scrubber reads object
data in strides, to avoid monopolizing the OSD's I/O capacity.
The default stride was set to 0.5MB, which is too low for
modern storage devices. This commit increases the default
stride to 4MB.

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>