fix: more warning when missing compiler plugins [APE-1491]

[antazoey]

What I did

fixes: #1222

I ran into this as well and got kinda confused for a minute!

This PR does the following to address the problem:

1. If after compiling, a manifest is empty, the user gets another warning
2. If trying to access a missing contract from a manifest, the IndexError is adjusted to also suggest you may be missing compiler plugins.

The full output looks like this now:

(ape310-pydanticv1) ➜  ape-safe git:(feat/safe-api) ✗ ape console                          
WARNING: Unprocessed plugin config(s): solidity. Plugins may not be installed yet or keys may be mis-spelled.

In [1]: project.dependencies["safe-contracts"]["1.3.0"]["GnosisSafe"]
WARNING: Compiled manifest produced no contract types! Are you missing compiler plugins?
ERROR: (ApeIndexError) Unable to find 'GnosisSafe' in 'safe-contracts'. Do you have the necessary compiler plugins installed?

In [2]: exit

You can see I was warned 3 times about stuff possible from missing compiler plugins.
Once at first because of an unprocessed config key. Another from compiling the dependency. And the final one, the IndexError, which I think is important, also asks me if I am missing a compiler plugin. It is important to be in the final error I believe because users always look there first.

How I did it

How to verify it

Checklist

• All changes are completed
• New test cases have been added
• Documentation has been updated