[#144] Optimizer improvements

Description

Some improvements of our optimizer:

1. Golden tests.
2. Small DROP optimizations (big optimizations are left for #299 (closed)).
3. Improved adjacentDips rule.
4. Remove redundant SWAP in case of commutative operations.

Related issue(s)

Resolves #144 (closed)

✅ Checklist for your Merge Request

Related changes (conditional)

• Tests (see short guidelines)

  • If I added new functionality, I added tests covering it.
  • If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • I checked whether I should update the docs and did so if necessary:
    • Root README and other README.md files
    • Haddock
    • docs/
  • I updated changelog files of all affected packages released to Hackage if my changes are externally visible.

Stylistic guide (mandatory)

• My commits comply with the following policy.
• My code complies with the style guide.