Add a `claim_drip` view to read accrued-but-unsettled (v4 patch)

[greatest0fallt1me]

Description

This is a smart-contract issue for the GrantFox campaign. Read-only view returning unsettled accrual per (stream, recipient).

Requirements and Context

• Implement per the description
• Add focused tests for the change
• Document any API/visible changes
• Adhere to repo's lint and code style
• Must be secure, tested, and documented

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b feature/claim-drip-view

2. Implement changes
3. Test and commit

Example commit message

feat: claim_drip read-only view

Acceptance Criteria

• Implementation matches the description
• Tests added and passing
• Code review approved
• Docs updated

Guidelines

• Clear documentation and inline comments
• Timeframe: 96 hours

[jaynomyaro]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!

[yunus-dev-codecrafter]

Hi! I've carefully reviewed the entire task description and fully understand the requirements and expected outcome.
I have experience working on similar tasks and I'm confident I can complete this within about an hour. I'd be happy to take ownership of this issue and submit a clean, well-tested solution promptly.
If it's available, please assign it to me. Thank you!