Optimize ReserveSample Function

[nugaon]

Task

Optimize the ReserveSample function in the Bee node to improve performance and reduce resource consumption. This function is critical for node operators participating in storage incentives, but currently runs too slowly to complete within required lottery round time constraints (issue #5132). Performance bottlenecks in sample fetching negatively impact node operators and contribute to higher staking requirements (issue #4849).

Acceptance criteria

• Sample generation completes within lottery round time constraints
• Reduced resource (CPU, memory etc.) usage during sampling process
• No regressions in sample correctness
• Performance metrics showing improvement compared to baseline