Add NDJSON streaming query support

[bplatz]

Summary

Adds HTTP streaming query support using NDJSON (Newline-Delimited JSON) format for efficient handling of large result sets. This enables progressive result rendering and reduces memory pressure on both server and client.

Implementation

Core Changes

• handlers/ledger.clj: Implemented ndjson-streaming-body function that converts core.async channels to Ring StreamableResponseBody, with proper exception handling and metadata support
• Handler routing: Modified query handler to detect Accept: application/x-ndjson header and route to streaming vs. buffered execution
• HTTP 206 status: Returns 206 Partial Content for streaming responses to bypass response coercion middleware

Streaming Behavior

• Results emitted as tuples (arrays) for efficiency: ["Alice", 30]
• Each result written as NDJSON line (one JSON value per line)
• Optional metadata tracking: final {"_fluree-meta":{"status":200,"fuel":...,"time":...}} line when tracking headers are present
• Stream closes when all results are emitted

Dependencies

• consensus/events.clj: Updated imports from deprecated fluree.db.ledger to fluree.db.transact namespace
• consensus/raft/handlers/new_commit.clj: Updated imports to use fluree.db.transact
• deps.edn: Updated fluree/db dependency to SHA 74fcc49d1154146cc0e66126322f3ad5b0047969
• task_test.clj: Replaced deprecated transact! with update! API

Testing

• streaming_query_test.clj: Comprehensive integration tests covering:
  • Basic NDJSON streaming with tuple results
  • Metadata tracking (fuel, time, policy)
  • Query LIMIT support
  • Comparison with buffered query behavior
  • 21 assertions, all passing

Documentation

• README.md: Added streaming query section with curl examples showing:
  • Basic NDJSON streaming usage
  • Query tracking headers for metadata
  • Key differences from buffered queries

Dependencies

This implementation builds on the fluree/db streaming query API introduced in:

• fluree/db PR: Add streaming query API with metadata tracking support db#1133

Test Results

1 tests, 21 assertions, 0 failures

All existing tests continue to pass with no regressions.