uplift customlogs package from evm repositories

[JonathanOppenheimer]

Why this should be merged

There are packages in subnet-evm and coreth that share a lot of functionality / are mirrored. As has been discussed as an evm team wide effort, we are working to uplift these packages to AvalancheGo to prevent the duplicative maintenance of two sets of the same code. This particular package, customlogs is a relatively easy lift.

Here are the packages being unified and uplifted:
coreth: https://github.com/ava-labs/coreth/tree/master/plugin/evm/customlogs
subnet-evm: https://github.com/ava-labs/subnet-evm/tree/master/plugin/evm/customlogs

How this was tested

This is currently 'dead' code; after a new AvalancheGo release is dropped, we can use the code in the evm repositories.

Need to be documented in RELEASES.md?

No

[Copilot]

Pull Request Overview

This PR uplifts the customlogs package from EVM repositories (subnet-evm and coreth) to AvalancheGo to eliminate duplicate maintenance. The package provides utility functions for working with Ethereum logs.

• Adds a new customlogs package under vms/evm/
• Introduces FlattenLogs utility function for converting nested log arrays

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[alarso16]

Seems weird to uplift untested code, but it seems slightly silly to test this

[joshua-kim]

nit: _ext filename suffix doesn't make sense in the context of avalanchego anymore

[joshua-kim]

I think the usage of this in core makes sense... but in filters we just use this to iterate over the logs and check if they match a filter (ref). We don't need to flatten the logs to do this... we could just iterate in 2-D. I feel like we could move this to core/blockchain.go pre-emptively instead and have it live as an unexported helper in that package where it is needed, and just update filters to just perform a 2-d iteration over the logs.