Upgrade Open Zeppelin versions, change max Solidity version

[drinkcoffee]

• Upgrade Open Zeppelin versions from 4.9.3 and 5.0.2 to 4.9.6 and 5.6.1.
• Change Open Zeppelin version specifiers in contracts to openzeppelin-contracts-4 or openzeppelin-contracts-5, so that minor Open Zeppelin version changes don't trigger mass source code changes.
• Change contracts from using @openzeppelin package to openzeppelin-contracts-4 to make it explicit which version they are using. Note that @openzeppelin is still needed as it is references from openzeppelin-contracts-upgradeable-4
• Upgrade some modules from 4.x to 5.x: payment splitter, deploy, guarded multicall
• Change max Solidity version from <0.8.29 to <=0.8.27.