DRAT Signature (#2757)

DRAT Signature (#2757)

* DRAT signature

Added the DRAT signature to CVC4.

We'll need this in order to compare three BV proof pipelines:
   1. DRAT -> Resolution -> Check
   2. DRAT -> LRAT -> Check
   3. DRAT -> Check (this one!)

Tested the signature using the attached test file. i.e. running
```
lfscc sat.plf smt.plf lrat.plf drat.plf drat_test.plf
```

* Added type annotations for tests

* Respond to Yoni's review

* Apply Yoni's suggestions from code review

Documentation polish

Co-Authored-By: alex-ozdemir <aozdemir@hmc.edu>
* Whoops, missed a spot or two