chore: make abigen offline by default, fix ethers-solc features

[DaniPopes]

Motivation

• ethers-contract-abigen is online by default in ethers-contract and ethers. If there are both ethers-contract-abigen as a build script, and ethers{-contract} with the abigen feature, then it will be built twice: once without online for the build script, and once with online. I'm not 100% sure about this, but that's what I've gathered from building Foundry a ton of times the past few days. This meant it also built its entire dependency tree, which includes ethers-etherscan -> ethers-solc (feature) -> solang-parser ... etc, so insane amount of work, duplicated.

• Multicall and other stuff gated by #[cfg(feature = "abigen")] in ethers-contract are not accessible with abigen-offline

• forward ethers-solc features from ethers-etherscan

Solution

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[mattsse]

I think this is reasonable.
this should discourage http abigen links which aren't very stable anyway due flaky etherscan API

ci failing, likely feature snafu
it's new solc version check: #2417