Add investor exposure cap tests (max_active_bids_per_investor and portfolio cap enforcement)

[Baskarayelu]

Description

Add tests that assert per-investor limits cannot be bypassed by bid churn (place/cancel/expire) and that exposure caps are enforced consistently.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested execution

• Fork the repo and create a branch
• git checkout -b feature/investor-exposure-cap-tests
• Implement changes
• Write contract: quicklendx-contracts/src/bid.rs, quicklendx-contracts/src/verification.rs, quicklendx-contracts/src/protocol_limits.rs
• Write comprehensive tests: quicklendx-contracts/src/test_bid.rs, quicklendx-contracts/src/test_protocol_limits.rs
• Add documentation: docs/contracts/limits.md
• Include NatSpec-style comments (Rust doc comments on public items)
• Validate security assumptions (caps reduce concentrated risk and limit abuse)

Test and commit

• Run tests
• cd quicklendx-contracts && cargo test --verbose
• Include test output and security notes

Example commit message

test: enforce investor exposure caps and active-bid limits

Guidelines

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

[drips-wave]

@Baskarayelu Savage27z could not be assigned to this issue because they have reached the maximum of 4 accepted assignments per organization in the current wave of the Stellar Wave Program.

The assignee has been removed. Please choose a different contributor.

[Martins-O]

@Martins-O has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Martins-O to this issue.

[drips-wave]

@Baskarayelu Martins-O could not be assigned to this issue because they have reached the maximum of 4 accepted assignments per organization in the current wave of the Stellar Wave Program.

The assignee has been removed. Please choose a different contributor.

[fairbid01]

@fairbid01 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

I would like to work on this issue because comprehensive exposure cap tests are critical for protocol security and prevent bid-churn exploits that could bypass per-investor limits. I'll implement tests in test_bid.rs and test_protocol_limits.rs covering max_active_bids_per_investor and portfolio cap enforcement across place/cancel/expire scenarios, add NatSpec documentation, and achieve 95%+ test coverage.
Thanks!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @fairbid01 to this issue.