Parallel PIRProcessDatabase

[glebfann]

Asynchronous Processing:

• Converted ProcessDatabase to support asynchronous execution by utilizing AsyncParsableCommand.
• Speeded up the execution of PIRProcessDatabase by adding asynchronous processing enabled through the --parallel flag with Swift concurrency.
  Also added Sendable conformance to several types to ensure safe concurrent access.

Enhanced Logging:

• Refined logging to include a prefix "Shard №(shardID):" for each log entry. This change addresses the non-sequential and interleaved nature of logs caused by asynchronous execution, making it easier to trace shard-specific activities.
• Example log entries:
  --no-parallel: https://pastebin.com/gWH1n9B7
  --parallel: https://pastebin.com/QCrQMvJX

Performance Comparison, with 2 million numbers in identity.binpb:

• Async Execution (time PIRProcessDatabase --parallel identity-config.json):
  1: real 0m11.638s, user 1m8.456s, sys 0m3.310s
  2: real 0m10.835s, user 1m8.368s, sys 0m3.242s
  3: real 0m10.833s, user 1m8.215s, sys 0m3.077s

• Sync Execution (time PIRProcessDatabase --no-parallel identity-config.json):
  1: real 0m52.301s, user 0m49.667s, sys 0m1.936s
  2: real 0m52.117s, user 0m49.544s, sys 0m1.961s
  3: real 0m51.489s, user 0m49.378s, sys 0m1.789s

The asynchronous execution with --parallel demonstrates a significant reduction in real execution time compared to the synchronous approach.

P.S. identity-config.json:

{
    "inputDatabase": "identity.binpb",
    "outputDatabase": "identity_data/identity/identity-SHARD_ID.bin",
    "outputPirParameters": "identity_data/identity/identity-SHARD_ID.params.txtpb",
    "rlweParameters": "n_4096_logq_27_28_28_logt_5",
    "sharding": {
        "shardCount": 20
    },
    "trialsPerShard": 1,
    "cuckooTableArguments": {
        "hashFunctionCount": 2,
        "maxEvictionCount": 100,
        "bucketCount": {
            "fixedSize": {
                "bucketCount": 10000
            }
        },
        "maxSerializedBucketSize": 1024
    }
}

[karulont]

Thank you for the PR!

Overall it looks good, just a few minor comments.