[LRAT] A C++ data structure for LRAT. (#2737)

[LRAT] A C++ data structure for LRAT. (#2737)

* [LRAT] A C++ data structure for LRAT.

Added a data structure for storing (abstract) LRAT proofs.

The constructor will take a drat binary proof and convert it to LRAT
using drat-trim. However, this is unimplemented in this PR.

Subsequent PRs will add:
   * LFSC representation of LRAT
   * Bitvector Proofs based on LRAT
   * Enabled tests for those proofs

* Documenting LRAT constructors

* Apply suggestions from code review

Co-Authored-By: alex-ozdemir <aozdemir@hmc.edu>
* Responding to Andres' review

Consisting of
   * Naming nits
   * Closed fds
   * Better implementation of disjoint union for LratInstruction
   * DRAT -> LRAT conversion is no longer an LratProof constructor

* include reorder

* Update src/proof/lrat/lrat_proof.h

Co-Authored-By: alex-ozdemir <aozdemir@hmc.edu>
* Addressed Andres' comments

* ANonymous namespaces and name resolution?

* Remove inlines, fix i negation

Thanks Andres!

* Use `std::abs`

Credit to Andres

Co-Authored-By: alex-ozdemir <aozdemir@hmc.edu>
* Remove uneeded public