docs: document correct order of locking for LedgerContext

[ozgb]

Overview

Follow-up from @Klapeyron's comment here: #1605 (comment)

Documents the correct order of aquisition for the mutexes in LedgerContext.

As part of this work, I verified that all current usage of the mutexes is correct.

🗹 TODO before merging

• Ready

📌 Submission Checklist

• All commits are signed off (git commit -s) for the DCO
• Changes are backward-compatible (or flagged if breaking)
• Pull request description explains why the change is needed
• Self-reviewed the diff
• I have included a change file, or skipped for this reason:
• If the changes introduce a new feature, I have bumped the node minor version
• Update documentation (if relevant)
• Updated AGENTS.md if build commands, architecture, or workflows changed
• No new todos introduced

🧪 Testing Evidence

Please describe any additional testing aside from CI:

• Additional tests are provided (if possible)

🔱 Fork Strategy

• Node Runtime Update
• Node Client Update
• Other:
• N/A

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