Add BLAKE3 hash algorithm option for Secure Seed

[GideonWhite1029]

Continuation of this PR: #414

Summary

• Adds HashingBlake3.java — a BLAKE3-inspired 64-bit implementation
  using only 4 rounds (vs 12 in BLAKE2b) and ThreadLocal state pooling
  for reduced allocations and improved throughput
• WorldgenCryptoRandom now dispatches to either algorithm at runtime
  based on config
• Adds hash-algorithm config option under misc.secure-seed:
  • blake2b (default) — original behaviour, unchanged
  • blake3 — faster alternative; fewer rounds
• Extends Secure Seed coverage to Mineshaft, NetherFortress, and
  NetherFossil structures

Config

misc:
  secure-seed:
    enabled: false
    hash-algorithm: blake2b   # blake2b | blake3

Tests

Lead time with Blake3:

Lead time with Blake2b: