(feat) Add Return and Propagate Fail Correctly

[AlSchlo]

What & Why

This PR adds a return operator in the HIR and in the Engine, and likewise fixes the behavior of Fails to propagate correctly up the call stack.

This has been implemented by adding a field to the Engine, which keeps track of the upper function call continuation.
Existing test cases have been adapted: (related to Fail), and a new one for Return has been added.

     // Define a function:
     // fn test_return(x: I64) = 
     //   let result = if x < 10 {
     //     return "too small"
     //   } else {
     //     "big enough"
     //   }
     //   "result is: " ++ result
     // }

Some Refactoring

• Made all eval functions member functions of Engine.

Follow-up Work (less urgent)

• Adding a return keyword in the AST and mapping it to the HIR.
• Adding the Rust-like ? operator to unwrap option types.
• For some unknown reason I had to make the Messages clonable, and had to make the one shot channel a shared channel. Any idea to avoid that? It doesn't seem like we really need the Clone bound, but removing it leads to errors.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.02193% with 364 lines in your changes missing coverage. Please review.

Project coverage is 79.4%. Comparing base (ad270d3) to head (dc8c3f5).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
optd-dsl/src/analyzer/error.rs	29.6%	211 Missing ⚠️
optd/src/catalog/iceberg.rs	0.0%	24 Missing ⚠️
...td-dsl/src/analyzer/semantic_check/cycle_detect.rs	85.0%	19 Missing ⚠️
optd-dsl/src/analyzer/semantic_check/adt_check.rs	98.0%	15 Missing ⚠️
optd-dsl/src/analyzer/from_ast/expr.rs	98.1%	14 Missing ⚠️
optd-dsl/src/compile.rs	0.0%	13 Missing ⚠️
optd-dsl/src/engine/eval/expr.rs	96.7%	13 Missing ⚠️
optd-dsl/src/cli/main.rs	0.0%	11 Missing ⚠️
optd-dsl/src/analyzer/types.rs	92.3%	10 Missing ⚠️
optd-dsl/src/analyzer/from_ast/pattern.rs	96.3%	9 Missing ⚠️
... and 10 more

Additional details and impacted files

Files with missing lines	Coverage Δ
optd-core/src/optimizer/mod.rs	0.0% <ø> (ø)
optd-dsl/src/analyzer/context.rs	89.0% <100.0%> (ø)
optd-dsl/src/analyzer/hir.rs	79.1% <ø> (+6.2%)	⬆️
optd-dsl/src/analyzer/map.rs	96.5% <100.0%> (-0.2%)	⬇️
optd-dsl/src/engine/eval/operator.rs	100.0% <100.0%> (ø)
optd-dsl/src/engine/utils.rs	100.0% <100.0%> (ø)
optd-dsl/src/lexer/lex.rs	97.9% <100.0%> (+<0.1%)	⬆️
optd-dsl/src/utils/error.rs	25.0% <ø> (ø)
optd-dsl/src/utils/tests.rs	91.1% <100.0%> (ø)
optd-dsl/src/analyzer/from_ast/converter.rs	98.4% <98.4%> (+0.5%)	⬆️
... and 19 more

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[yliang412]

For some unknown reason I had to make the Messages clonable, and had to make the one shot channel a shared channel. Any idea to avoid that? It doesn't seem like we really need the Clone bound, but removing it leads to errors.

I think it's because Engine<O> and if we want the engine to be clonable, then you have to make the continuation clonable.