StakeStakeV2 zero copy api [wincode]

[grod220]

Adds a new zero‑copy state API backed by wincode.

Key Changes

• Adds p-stake-interface crate (#![no_std] compatible)
• Integrates alignment-1 POD types for safe zero-copy from unaligned slices
• New API via StakeStateV2:
  • StakeStateV2::from_bytes(&[u8]) -> Result<&StakeStateV2, StakeStateError> for read-only access
  • StakeStateV2::from_bytes_mut(&mut [u8]) -> Result<&mut StakeStateV2, StakeStateError> for
    mutations
  • Tag-checked accessors: meta(), stake(), meta_mut(), stake_mut()
  • State transitions: initialize(), delegate()
• Maintains full ABI compatibility with legacy bincode-encoded stake accounts

Motivation

Deserialization via bincode/borsh is computationally expensive for programs that only need to access specific fields or verify the state. This zero-copy approach allows for significantly lower compute unit (CU) usage when interacting with stake accounts.

[joncinque]

Looks great overall! Mostly small things on my side

[febo]

I got a few more small comments.