Implement rate limiting for outbound RPC calls in the CLI to prevent unintentional RPC provider abuse

[ALLEN-AYODEJI]

Description

The CLI has no rate limiting on stellar RPC calls. In a scripted workflow (e.g., polling agreement status in a loop), the CLI could send hundreds of requests per second to the Stellar RPC endpoint, potentially exceeding rate limits and getting the user's IP banned. A configurable rate limiter prevents unintentional abuse.

Requirements and context

• Security: Standard security review required for state-mutating changes
• Testing: Full test suite must pass; new tests for changed behavior
• Documentation: Update doc comments and README if user-facing

Suggested execution

Branch: fix/feat/security-rate-limiting

Implement changes

• Add a rate limiter using governor or similar crate that limits to N requests per second
• Default limit: 10 requests/second (adjustable via STELLAR_RPC_RATE_LIMIT env var)
• Queue requests that exceed the rate limit and execute them when the window resets
• Log a warning when rate limiting is actively throttling requests

Test and commit

Test by sending 100 rapid requests — verify only 10/s go through and the rest are queued. Test with rate limit set to 0 (unlimited). Run cargo test.

Example commit message

feat(cli): add configurable outbound RPC rate limiting to prevent provider abuse

Guidelines

• Open a PR against master
• Keep PR focused on this single concern
• Run cargo test or npm test before review
• Ensure no lint or typecheck warnings