fix(solc): traverse nodes iteratively

[mattsse]

Motivation

Nodes were traversed recursively which could Hit a SO on large repos, like https://github.com/fei-protocol/tribe-turbo

Solution

Use an iterator NodesIter instead that yields all nodes instead

PR Checklist

• Added Tests
• Added Documentation
• Updated the changelog

[gakonst]

lgtm - it does seem like these SO's are hard to unit test, so guess the best way is to add such repos in the integration tests in upstream foundry, or add integration tests for ethers-solc itself