Add clj-kondo exports and config, fix linting errors, some addt'l fixes

[k13gomez]

Hi Chris,
In this PR I've included the following changes:

• Add clj-kondo exports and config, fix linting errors
• Remove support for and call to take-last 1-arity, which was not valid.
• Fix variable arity merge-with, which was not correctly implemented.

Just adding linting some syntax/arity errors became visible and I fixed them, but there could be other issues due to lack of testing, so I'd like to help out to expand testing for the project, to that end I'd like your opinion on the following plan:

• Swap the tests runner to kaocha, this will allow easy integration with multiple plugins, as well as split the tests by category (performance vs unit tests, etc, see this project for example: https://github.com/k13labs/clara-rules/actions/runs/8090904763/job/22109138392).
• Add test coverage using clovegage plugin for kaocha, this would only run on tests that do not measure performance, as instrumenting namespaces with coverage naturally reduces performance.
• Once the codebase is instrumented with coverage reporting, then it becomes easier to add more tests and increase coverage in the areas that are lacking testing.

[cnuernber]

Honestly this all sounds great - one thing I noticed is the fixes around the protocol implementation. This implementation isn't complete but I needed a project with a repl to implement 85% or so of the protocol changes. The full changes exist in my cn-master branch of clojure. I may remove the implementation and the tests from this project as cn-master is stable.

[k13gomez]

Sounds good, I won't spend much time around the defprotocol namespace, but mainly wanted to get rid of any linting issues to get the project to a point where we could start linting in the GH Actions and fail builds if lint errors are found.

[cnuernber]

Sure - makes sense!