feat: Engine CPS

[AlSchlo]

Making the engine CPS so that it fits properly with the optimizer pub/sub model.

This is in fact a simplication of the codebase.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 81.67098% with 283 lines in your changes missing coverage. Please review.

Project coverage is 73.3%. Comparing base (03e6b1d) to head (deec19a).

Files with missing lines	Patch %	Lines
optd-core/src/engine/mod.rs	2.9%	99 Missing ⚠️
optd-core/src/optimizer/subscriptions.rs	0.0%	74 Missing ⚠️
optd-core/src/optimizer/generator.rs	0.0%	42 Missing ⚠️
optd-core/src/optimizer/handlers.rs	0.0%	23 Missing ⚠️
optd-core/src/engine/eval/expr.rs	95.0%	21 Missing ⚠️
optd-core/src/optimizer/ingest.rs	0.0%	20 Missing ⚠️
optd-core/src/optimizer/mod.rs	0.0%	2 Missing ⚠️
optd-core/src/engine/eval/binary.rs	0.0%	1 Missing ⚠️
optd-core/src/engine/eval/mod.rs	96.5%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
optd-core/src/bridge/from_cir.rs	0.0% <ø> (ø)
optd-core/src/engine/eval/core.rs	100.0% <100.0%> (+9.9%)	⬆️
optd-core/src/engine/eval/match.rs	99.0% <ø> (+4.6%)	⬆️
optd-core/src/engine/eval/operator.rs	100.0% <100.0%> (+67.1%)	⬆️
optd-core/src/engine/test_utils.rs	100.0% <100.0%> (ø)
optd-core/src/engine/utils.rs	100.0% <100.0%> (ø)
optd-core/src/engine/eval/binary.rs	80.7% <0.0%> (ø)
optd-core/src/engine/eval/mod.rs	96.6% <96.5%> (ø)
optd-core/src/optimizer/mod.rs	0.0% <0.0%> (ø)
optd-core/src/optimizer/ingest.rs	0.0% <0.0%> (ø)
... and 5 more

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[connortsui20]

I'm thinking we merge this immediately so that it doesn't block anyone else. It's not super useful for me to force the review loop now imo. Also, at a first glance there's nothing suspicious here anyways so I think this is fine to merge now.

What I'll probably do is make a separate PR that cleans up some of the documentation (mainly so I can get a better understanding of everything, but also to clean up).

[yliang412]

Great to have the mock tests!