Update solidity contracts

The pragma version on the current version of the contract is years out of date.

The issue does not name the contract files, current pragma, target Solidity version, or tests. Start by locating the repository's Solidity contracts and checking their pragma declarations, then establish the supported target version from the project context. Done means the relevant contracts use the agreed current pragma and the available project checks pass.

Written by the indexing model from the issue text.