alt_bn128 Syscall

A native Solana runtime syscall providing elliptic curve operations on the alt_bn128 (BN254) curve — specifically point addition, scalar multiplication, and pairing checks. These operations are essential for on-chain Groth16 zk-SNARK proof verification, which would otherwise exceed the 1.4M compute unit limit if implemented in pure BPF bytecode. Light Protocol's compressed account verification and Token-2022's confidential transfers both depend on the alt_bn128 syscall for ZK proof verification within practical compute budgets.