(feat) Type Inference Bounds

[AlSchlo]

quick overview

This PR is the next step for type inference in our DSL, and follows #72 .

To solve the constraints, we need two core functions: greatest_lower_bound and least_upper_bound.

• The least upper bound is the most specific type that is a supertype of both input types.
• The greatest lower bound is the most general type that is a subtype of both input types.
  See tests for examples.

Furthermore, some code in types.rs was broken, but is now fixed.

• Map key was not contravariant, but covariant.
• T was not a subtype of Optional[T].

next steps

Writing the solver is the next and final step for practical type inference. We would still need to handle Generics properly, and propagate Costed/Stored.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.59571% with 19 lines in your changes missing coverage. Please review.

Project coverage is 80.5%. Comparing base (665f98b) to head (d00d99e).

Files with missing lines	Patch %	Lines
optd-dsl/src/analyzer/type_infer/glb.rs	97.8%	11 Missing ⚠️
optd-dsl/src/analyzer/type_infer/lub.rs	98.9%	8 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
optd-dsl/src/analyzer/types.rs	96.3% <100.0%> (+0.3%)	⬆️
optd-dsl/src/analyzer/type_infer/lub.rs	98.9% <98.9%> (ø)
optd-dsl/src/analyzer/type_infer/glb.rs	97.8% <97.8%> (ø)

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