Add the batch job store to internal/dcache (storage only; no HTTP, no worker).
New internal/dcache/batch.go holds the BatchJob/BatchTarget types and all
accessors; Open gains the batch_job/batch_target tables and indices, and DB
gains BatchH/BatchM counters.
Sliding lease: writes (UpdateBatchTarget, SetBatchJobStatus, TouchBatchJob,
MarkInFlightFailed) bump the job lease to now; reads never write. BatchJobByIDem
returns the newest (caller, idem_key) job with lease+ttl>now and status
queued/running/done/partial. UpdateBatchTarget counts targets_done exactly once
per target entering done/failed and adds len(result) to nbytes. SweepBatch
removes by lease; EvictBatchOldest evicts whole non-live jobs oldest-lease-first;
MarkInFlightFailed reconciles in-flight jobs on restart. Batch nbytes are kept out
of Size() and the content evict union.
Co-Authored-By: ornith-1.5-35b-a3b <ornith-1.5-35b-a3b@llama.cpp.invalid>
kyleandornith-1.5-35b-a3b
2529cb8e84