feat: unstake

[roberts-pumpurs]

Describe the changes

A user with no pledges and active stake can unstake. refund will be given out at the epoch block. immediate tx inclusion costs a fixed fee.

Unstaking is now a 2 step process:

• split unstake handling into fee-only inclusion debits and epoch refund credits, add the UnstakeDebit packet type, and adjust shadow transaction execution paths and unit tests.
  • Affected files: crates/actors/src/shadow_tx_generator.rs, crates/irys-reth/src/shadow_tx.rs, crates/irys-reth/src/evm.rs, crates/irys-reth/src/lib.rs
• derive UnstakeRefundEvents alongside unpledge refunds so epoch blocks repay stakers only after pledges clear, and reuse the same logic during block validation.
  • crates/actors/src/block_producer.rs, crates/actors/src/block_validation.rs, crates/actors/src/commitment_refunds.rs

Snapshots:

• extend commitment snapshots to track pending unstake requests, block duplicates, and reject attempts while pledges remain active; epoch processing now applies unstakes with explicit errors for inconsistent state.
  • crates/domain/src/snapshots/commitment_snapshot.rs, crates/domain/src/snapshots/epoch_snapshot/epoch_snapshot.rs, crates/actors/src/block_discovery.rs, crates/actors/src/mempool_service/commitment_txs.rs

Mempool:

• include all commitment types in the scheduling pipeline and surface validation errors when commitments are dropped. Previously unstake txs were blocked.

Misc:

• (if anyone is using nix) crates/c/build/capacity.rs: honor NIX_ENFORCE_NO_NATIVE by skipping -march=native when the environment requests it.
• fix issue where commitment tx fee was applied twice (bug in shadow tx generator)

Tests:

• crates/chain/tests/block_production/unstake_refund.rs, crates/chain/tests/validation/unstake_edge_cases.rs add end-to-end coverage for unstake refunds, rejection scenarios, and updated fee expectations.

Checklist

• Tests have been added/updated for the changes.
• Documentation has been updated for the changes (if applicable).
• The code follows Rust's style guidelines.

[DanMacDonald]

This looks solid 👍. Some minor (optional) nits.