Add regulatory-limit event stream so indexers can rebuild aggregate cap usage per jurisdiction

[greatest0fallt1me]

Description

Emit a reg_limit_delta event on each holding change so indexers can rebuild aggregate cap usage per jurisdiction over time. Required for periodic Reg D and Reg S reporting.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review
• Relevant code: src/test_transfer_restrictions.rs, indexer/
• Event must include jurisdiction, delta, and new aggregate

Suggested execution

• Fork the repo and create a branch
• git checkout -b feat/reg-limit-event
• Implement changes
  • Emit reg_limit_delta on issuance and transfer
  • Add indexer fixture
  • Document field ordering
• Validate security and correctness assumptions

Test and commit

• Run tests
  • cargo test --all
• Cover edge cases
  • Transfer between two holders in the same jurisdiction (no delta)
• Include test output and security notes

Example commit message

feat: emit reg_limit_delta events for jurisdiction caps

Guidelines

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 96 hours

[obswrld]

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@obswrld's PR #698 was approved and merged by @thlpkee20-wq.

🏆 @obswrld: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (481 total points). Track your full progress on GrantFox.

👏 Great work, @obswrld! Keep contributing to RevoraOrg.

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This issue has been completed by @obswrld as part of the Stellar Wave Program's 7th Wave 🥳

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