* fix ec.encode skipping volumes when one replica is on a full disk
This fixes issue #8218. Previously, ec.encode would skip a volume if ANY
of its replicas resided on a disk with low free volume count. Now it
accepts the volume if AT LEAST ONE replica is on a healthy disk.
* refine noFreeDisk counter logic in ec.encode
Ensure noFreeDisk is decremented if a volume initially marked as bad
is later found to have a healthy replica. This ensures accurate
summary statistics.
* defer noFreeDisk counting and refine logging in ec.encode
Updated logging to be replica-scoped and deferred noFreeDisk counting to
the final pass over vidMap. This ensures that the counter only reflects
volumes that are definitively excluded because all replicas are on full
disks.
* filter replicas by free space during ec.encode
Updated doEcEncode to filter out replicas on disks with
FreeVolumeCount < 2 before selecting the best replica for encoding.
This ensures that EC shards are not generated on healthy source
replicas that happen to be on disks with low free space.
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