Add Benchmark for High Investor Count Scenario

[teeschima]

Closes #48

Description

This PR introduces benchmark‑style tests for scenarios with large investor sets in the escrow module. The goal is to evaluate storage growth and method behavior under realistic scale conditions.
Key Changes

Benchmark Implementation

    Added high‑cardinality investor scenario benchmark in escrow/src/test.rs.

    Simulates large investor sets to stress test storage and transaction handling.

Documentation

    Updated README.md with details on benchmark assumptions, methodology, and expected outcomes.

    Included notes on data structure limits and scalability considerations.

Testing

    Edge cases covered (e.g., maximum investor count, overflow scenarios).

    Minimum 95% test coverage ensured.

    Test output included with security notes on potential risks under extreme load.

Benchmark Assumptions

Investor count scaled to upper realistic limits.

Storage growth measured against expected linear/logarithmic patterns.

Validated against data structure constraints to ensure no overflow or corruption.

Security Notes

Benchmarks avoid exposing sensitive data.

Tests confirm that large investor sets do not compromise escrow integrity.

Documented potential risks if investor counts exceed tested thresholds.