feat: add transaction context crate

[bmuddha]

What changed

Customized the imported solana-transaction-context baseline for the engine's
account representation and patched the crate into the workspace.

Why

VM handlers need to remap account data on writes through a mapped region instead
of copying through a serialized input buffer.

Closes #10.

Impact

• Reshapes TransactionContext, InstructionContext, and
  TransactionAccounts around AccountRef and AccountRefMut views.
• Keeps accounts in UnsafeCell behind explicit borrow counters so borrows stay
  local to the context.
• Returns keyed accounts, return data, touched-account count, and resize deltas
  through ExecutionRecord.

Reviewer notes

Borrow counters are released on drop; outstanding references must be gone before
a context is deconstructed. The mapped-account divergences are documented in
solana/README.md.

Follow-up

program-runtime and svm consume this customized context 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
• 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 👈 (View in Graphite)
• feat: forked transaction-view for increased limits #33
• feat: add customized solana-account crate #13
• chore: import upstream Solana runtime crates #31
• master

This stack of pull requests is managed by Graphite. Learn more about stacking.

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