SIMD-0337: Markers for Alpenglow Fast Leader Handover, DATA_COMPLETE_SHRED placement rules

Active on mainnet-beta (epoch 1005), testnet (epoch 978) and devnet (epoch 1095).

Minimum versions: Agave v4.1.0-beta.0, Firedancer v1.0, Frankendancer v0.1001.40101.

Introduced in anza-xyz/agave PR #12075.