Catch reshard on producing an invalid result on encode.
This makes it much easier to catch errors.

This PR is not intended to be merged. It is a helper to verify #62816.

Replication steps:
1.
Deploy 5-6 OSD vstart cluster
2.

./bin/ceph osd erasure-code-profile set myecprofile k=2 m=1
./bin/ceph osd pool create ecpool 16 16 erasure myecprofile
./bin/ceph osd pool set ecpool allow_ec_overwrites true

fio --ioengine=rados --pool=ecpool --touch_objects=0 --clientname=admin --conf=ceph.conf --time_based --runtime=1h --iodepth=64 --numjobs=8 --group_reporting=1 --rw=randwrite --file_service_type=pareto:0.20:0 --bssplit=4k/16:8k/10:12k/9:16k/8:20k/7:24k/7:28k/6:32k/6:36k/5:40k/5:44k/4:48k/4:52k/4:56k/3:60k/3:64k/3 --size=50000M --nrfiles=12500 '--filename_format=stress_obj.$jobnum.$filenum' --name=test-ec-esb

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