feat: adds top level engine crate for global orchestration

[bmuddha]

What changed

Added the top-level magicblock-engine crate that wires keeper state,
transaction processing, block pacing, recovery, and MagicRoot account operations
behind the consumer-facing Engine handle.

Why

Embedding services need one entry point for opening durable state, reconstructing
it after recovery, submitting work, and coordinating shutdown.

Part of #4.

Closes #29.

Impact

• Engine::account exposes committed create, update, patch, and delete
  operations; Engine::transaction supports execute, schedule, and simulation.
• Instruction slices and Message values are signed with the engine authority
  and latest blockhash; sanitized views and encoded transactions are accepted
  without re-signing.
• Startup restores keeper state, replays retained entries after a snapshot rewind,
  and starts the sequencer with internal or external block pacing.
• Coordinated shutdown rejects new transactions, drains execution, and flushes
  durable or externally mirrored state according to the pacing source.

Reviewer notes

Replay quiesces at each sealed superblock and compares the reconstructed account
checksum with the recorded seal. Divergence returns
ReplayError::StateMismatch.

Follow-up

The replication crate uses the external pacer and replay paths to build followers
upstack.

[bmuddha]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat: add state replicator crate on top of the engine #25
• feat: adds top level engine crate for global orchestration #24 👈 (View in Graphite)
• feat: added internal built-in magic root program #23
• feat: implement transaction processor crate #22
• feat: implements keeper crate - state orchestrator #17
• feat: implement superblock based ledger crate #15
• feat: add optimized accountsdb crate #14
• feat: add nucleus engine crate #18
• feat: add svm crate #21
• feat: add program runtime crate #20
• feat: add transaction context crate #19
• feat: forked transaction-view for increased limits #33
• feat: add customized solana-account crate #13
• chore: import upstream Solana runtime crates #31
• master

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