Preserve directory structure, ignore tests, etc. refactoring for ethers-contract-abigen

[meetmangukiya]

Is your feature request related to a problem? Please describe.

Currently, it seems like we generate bindings either as multiple files or single file depending on args, if single file, everything is written to a single file, if multiple file, we create one file per contract and include those in lib.rs or mod.rs depending on what the user selected, to generate a crate or a module.

Tried this out recently, but see a few problems(?):

1. Everything is generated at top level src/..contract.rs, not quite nice.
2. Everything in artifacts dir gets generated, usually we'd want to ignore the contracts defined in :tests/ or :src/tests.

Describe the solution you'd like

1. src/... contracts get generated in same directory structure as in source and follows same module structure.
2. lib/... contracts get generated the same way as in 1, but under a reserved dir like vendor / third_party directory

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Additional context Add any other context or screenshots about the feature request here.