gnark-solana verifier OOM on Solana: heap allocations inside prepare_inputs()

[tanctl]

Description
In gnark-solana/crates/verifier-lib/src/verifier.rs:157–172, prepare_inputs() allocates temporary Vec buffers per public input using .concat() and syscall helpers that return Vec. On Solana the program heap is a bump allocator that does not free during execution, so these allocations accumulate and can exhaust the ~32 KiB heap, causing memory allocation failed, out of memory and a program panic on proofs with enough public inputs.

Suggested fix
Remove heap allocation from the hot path: build syscall input buffers on the stack (eg, [u8; 96] and [u8; 128]) and return fixed-size arrays (eg, [u8; 64]) instead of Vec, keeping heap usage flat and preventing OOM.