Add freeze-reason-scoped unfreeze allowing partial thaw when only one reason is cleared

[thlpkee20-wq]

Description

When multiple freeze reasons apply, clearing one should not automatically unfreeze the account. Add reason-scoped unfreeze semantics that only thaws when all reasons are cleared.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review
• Relevant code: src/test_freeze_matrix.rs
• Reason set persisted as bitmask under FreezeReasonSet

Suggested execution

• Fork the repo and create a branch
• git checkout -b feat/freeze-scoped-unfreeze
• Implement changes
  • Persist reason bitmask
  • clear_freeze_reason(reason) clears bit and re-evaluates
  • Emit freeze_reason_cleared event
• Validate security and correctness assumptions

Test and commit

• Run tests
  • cargo test --all
• Cover edge cases
  • Clear the only-set reason (full unfreeze)
• Include test output and security notes

Example commit message

feat: scoped-unfreeze by reason bitmask

Guidelines

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

[Gentleslyl2006]

Hello maintainer
I can fix this issue.
Can I get it assigned