Consider using named mappings for improved code readability

The contract uses traditional mapping syntax instead of the more readable named mapping syntax introduced in Solidity 0.8.18:

// Current implementation
mapping(uint => Position) public positions;
mapping(address => uint[]) public positionIdsByAddress;
mapping(uint => uint) public tiers;

Named mappings make the code more self-documenting by explicitly stating what the keys and values represent.

Update to latest stable Solidity version and use named mappings:

// More readable implementation
mapping(uint positionId => Position position) public positions;
mapping(address user => uint[] positionIds) public positionIdsByAddress;
mapping(uint daysLocked => uint basisPoints) public tiers;

This improves code readability, self-documentation, maintenance and auditing, and function-parameter consistency (names can match mapping key/value names).