[WIP] Batch kernel MASM implementation

[krushimir]

Summary

Initial implementation of the batch kernel in MASM for proving transaction batches.

⚠️ Draft - not ready for review yet. Opening for visibility on progress.

Required Checks

• Transaction list not empty
• Transaction ids are not duplicated
• Account state correctly updated (A→B→C ordering via LinkMap)
• Account updates do not exceed MAX_ACCOUNTS_PER_BATCH
• All transaction expiration blocks > batch reference block
• batch_expiration_block_num = min(transaction expiration blocks)
• Input notes not duplicated (no duplicate nullifiers)
• Input/output note counts do not exceed limits
• Erase consumed unauthenticated notes (note erasure)
• Authenticate input notes with MMR proofs
• Transaction verification stub (tx_id as commitment)

Implementation Tasks

• Extract LinkMap from transaction kernel to shared module
• Add batch kernel to miden-protocol, build.rs, export BatchKernel struct
• Add utility functions (stack inputs, advice inputs, parse outputs)
• Prologue: "Unhash" inputs, load everything from advice
• Verify TRANSACTIONS_COMMITMENT hash
• Account validation: Delta merging via LinkMap
• Note validation: BatchNoteTree (SMT), note erasure
• Epilogue: Compute real output commitments
• Add ExecutionProof to ProvenBatch

Closes #1122