#2974: Add hash-based journal selection for improved ledger distribution

[jprieto-temporal]

Main Issue: #2974

Motivation

When multiple journals are configured, BookKeeper selects a journal using ledgerId % numJournals. This works well when
ledger IDs are random or sequential, but produces poor distribution when ledger IDs follow strided patterns (e.g., when
multiple clients allocate IDs from disjoint ranges). Uneven journal utilization can cause hotspots and reduce write
throughput.

Changes

• Add journalHashBasedSelection configuration option (default: false)
• When enabled, use Fibonacci hashing on ledger IDs before journal selection
• The hash function multiplies by the golden ratio constant and folds high bits into low bits to break predictable
  patterns
• Add integration test verifying read/write correctness with hash-based selection