5.1.2

• Faster u64 serialization by handling small numbers differently

Benchmark below. Protobuf does not deserialize into bigint so these benchmarks are not easily comparable.

borsh u64 with bigint x 5,385,093 ops/sec ±0.44% (389 runs sampled)
protobujs u64 with bigint x 7,022,500 ops/sec ±0.53% (393 runs sampled)
borsh u64 with number x 6,124,037 ops/sec ±0.42% (393 runs sampled)
protobujs u64 with number x 4,639,581 ops/sec ±0.35% (394 runs sampled)