Filestore cache cleaner performance tweaks

[djeebus]

• delete 900 files per loop (up from 100)
• only remove a single file entry from cache, not the whole listing

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Note

Adds configurable filestore cleanup (disk target, dry-run, files/deletions per loop) and updates cleaner to remove single cache entries; aligns Nomad job/CLI flags.

• IaC (Terraform/Nomad):
  • Filestore cleanup config: Replace filestore_max_disk_usage_target with filestore_cache_cleanup_disk_usage_target and add filestore_cache_cleanup_dry_run, filestore_cache_cleanup_files_per_loop, filestore_cache_cleanup_deletions_per_loop in iac/provider-gcp/* with validations/defaults.
  • Nomad job args: Update jobs/clean-nfs-cache.hcl to parameterize --dry-run, add --files-per-iteration and --deletions-per-iteration, and pass new vars in nomad/clean-nfs-cache.tf.
• Orchestrator (clean-nfs-cache):
  • CLI flags: Rename --max-files-per-iteration to --deletions-per-iteration.
  • Cache behavior: ListingCache.Decache now removes only the specific file from the cached directory listing; add removeByIndex helper.
  • Tests: Add unit tests for Decache and removeByIndex.

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