LIT-2954 - Update ILitNodeClient interface to match implementation

[MaximusHaximus]

Description

Ref: (3) described in this post: LIT-Protocol/Issues-and-Reports#9 (comment)

The function signature of handleNodePromises() has changed at some point in the past, but the interface is using a simpler signature.

This PR:

• Updates the ILitNodeClient interface to match the core implementation
  • This includes updating the type of serverKeys and connectedNodes to be accurate
• Makes LitNodeClientNodeJs implement the interface, so in the future if they get out of sync we will know about it.
  • This means that LitNodeClient also implements it, as it extends LitNodeClientNodeJs
• Ran eslint --fix on the files impacted by these changes
• Made the constructor type of LitNodeClient no longer a union with any 🎉

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Built all packages, ran all e2e tests

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[Ansonhkg]

lgtm!