feat: add transaction context crate

[bmuddha]

What changed

Added the solana-transaction-context crate, an engine-shaped fork of Agave's
crate patched in workspace-wide via [patch.crates-io].

Why

Engine execution needs the low-level structures it runs over, reshaped so VM
handlers can remap account data on writes through a mapped region instead of
copying through a serialized input buffer.

Closes #10.

Impact

• Introduces TransactionContext, InstructionContext, and the
  TransactionAccounts store with AccountRef/AccountRefMut views.
• Accounts live in UnsafeCell behind explicit borrow counters, keeping borrows
  local to the context.
• ExecutionRecord returns keyed accounts, return data, touched-account count,
  and account resize delta; TransactionAccounts tracks resize and per-instruction
  lamports deltas.

Reviewer notes

Borrow counters are released on drop; outstanding references must be gone before a
context is deconstructed (Rc::try_unwrap failures there are real lifetime bugs).
Divergences are documented in solana/README.md (Transaction Context, VM Account
Mapping, Access-Violation Growth).

Follow-up

program-runtime and svm build on this crate 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: 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: add customized solana-account crate #13
• master

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

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Free

Run ID: 92fa47c9-1c28-4bd7-b07a-f462ef424103

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Note

🎁 Summarized by CodeRabbit Free

Your organization is on the Free plan. CodeRabbit will generate a high-level summary and a walkthrough for each pull request. For a comprehensive line-by-line review, please upgrade your subscription to CodeRabbit Pro by visiting https://app.coderabbit.ai/login.

_{Comment @coderabbitai help to get the list of available commands and usage tips.}