[kwsantiago]

Brings follow_blake2b in line with the BOLT changes just merged into lightning-blake2b/bolts, and fixes a BOLT 12 interop failure with Core Lightning.

• Coinbase funding (BOLT 2): a fundee fails a channel whose funding transaction is a coinbase unless it is zero-conf (by channel_type or a trusted minimum_depth of 0), and we do not fund a channel from a coinbase ourselves. A spend of a coinbase output does not relay for far longer than its maturity on this network, so the channel's commitment transactions could not be broadcast while its HTLCs expire.
• Splicing (BOLT 2): no splice of a channel without option_unified_sigs. splice_channel and funding_contributed refuse, and an inbound splice_init or tx_init_rbf is answered with tx_abort after the usual validation, leaving quiescence as any abort does. Together with the existing refusal on unified channels, no channel is spliced while follow_blake2b is set.
• Gossip (BOLT 7): we do not announce a channel funded below the chain's BLAKE2b activation height. The check is shared with the existing gossip floor.
• Router: a one-hop blinded path (the introduction node is the recipient) now applies payinfo.cltv_expiry_delta. BOLT 4 has the recipient fold its min_final_cltv_expiry_delta into that value; LDK ignored it, so a payment to Core Lightning, which advertises 10, failed whenever LDK's random CLTV padding was smaller. simple_blinded_route_hints asserted the old value for one hop and now asserts the advertised one.

No public API changes beyond the existing follow_blake2b: no new variants, and the changed splice_init/tx_init_rbf signatures are crate-private.

Tests: cargo test --workspace passes, every commit builds, fuzz tests pass, and c_bindings, taproot and no-std check clean. New tests in blake2b_tests.rs and scid_utils.rs. Against Core Lightning v26.06.9 on Knots regtest with BLAKE2b active, a Lampo node built on this stack opens a unified channel, pays and is paid over BOLT 11 and BOLT 12, and closes cooperatively, in 5 of 5 runs.