chore: Add @typescript-eslint/no-confusing-void-expression rule

[teogeb]

Added new eslint rule: https://typescript-eslint.io/rules/no-confusing-void-expression/

This rule disallows e.g. using return foobar() when foobar() method returns void. It is better to just call the method and do explicit return separately, if needed. (Quite typically the return is not needed at all as the line is the last line of the method.)

Simplified multiple-publisher-plugins.test.ts so that it uses Promise<void> instead of Promise<unknown> and therefore doesn't need any special handling related to this rule.

[juslesan]

Why does this rule need to be ignored in Promise.all calls and some other places?

[teogeb]

Why does this rule need to be ignored in Promise.all calls and some other places?

It would be better to refactor these tests. In practice, the arguments sent to Promise.all() are evaluated before the Promise.all() call (like we do for all function calls: we need the value for parameters before we can pass those as arguments). Therefore it would be clearer if we'd move void calls out from Promise.all(), i.e. execute the lines explicitly before the Promise.all() is called.

[juslesan]

Could move the void expressions above the Promise.all blocks in all cases to get rid of the eslint-disable comments