bump to Rust 2024 edition

[connortsui20]

Problem

Bumps the rust edition to 2024.

Summary of changes

I just ran cargo fix --edition for 2024, and there were very few changes needed.

Rationale

This isn't just about being stale, this would make writing the rule engine SO MUCH easier. Notably async closures would help quite a lot with all of the continuations in the rule engine (the verbosity right now makes it hard to grok). There is basically no hope for someone trying to contribute to the rule engine who doesn't understand how futures in Rust works...

Also once this gets stabilized things become so much nicer: rust-lang/rust#138424 (it would mean we don't have to have the UnitFuture type alias and Box::pin all of our continuations with the dyn Trait coercions).

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.3%. Comparing base (0f6379f) to head (93fa76b).

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/bridge/into_cir.rs	0.0% <ø> (ø)
optd-core/src/engine/eval/binary.rs	80.7% <ø> (ø)
optd-core/src/engine/eval/core.rs	100.0% <ø> (ø)
optd-core/src/engine/eval/expr.rs	95.1% <ø> (ø)
optd-core/src/engine/eval/match.rs	99.0% <100.0%> (+<0.1%)	⬆️
optd-core/src/engine/eval/mod.rs	96.6% <ø> (ø)
optd-core/src/engine/eval/operator.rs	100.0% <ø> (ø)
optd-core/src/engine/eval/unary.rs	80.8% <ø> (ø)
optd-core/src/engine/mod.rs	6.4% <ø> (ø)
... and 18 more

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