Incremental compiler panics on C-LEARN model (catch_unwind workaround)

[bpowers]

Description

The incremental compiler (salsa-based compile_project_incremental) panics when processing certain models, most notably C-LEARN. Multiple call sites work around this by wrapping calls in std::panic::catch_unwind:

• benches/compiler.rs:71-80 -- the is_simulatable function explicitly documents that "some models (e.g. C-LEARN) panic in the incremental compiler rather than returning a clean error"
• tests/simulate.rs:1296 -- the cross-validation test loop wraps incremental compilation in catch_unwind to allow the test to continue past panicking models
• src/analysis.rs:122-124 -- LTM analysis wraps the pipeline for "graceful degradation"
• src/layout/mod.rs:1874, 2041, 2061, 2129 -- multiple layout functions wrap incremental/monolithic compilation

The monolithic compiler handled these same models without panicking, so the issue is specific to the incremental compilation path.

Why it matters

• Correctness: Panics indicate unhandled states that should be proper errors
• WASM safety: catch_unwind is ineffective under panic = "abort" (used in WASM release builds), so these models would crash the entire WASM runtime rather than failing gracefully
• Maintainability: catch_unwind is not a substitute for proper error handling and makes it harder to reason about failure modes

Components affected

• src/simlin-engine/src/db.rs (incremental compilation entry points)
• src/simlin-engine/benches/compiler.rs
• src/simlin-engine/tests/simulate.rs
• src/simlin-engine/src/analysis.rs
• src/simlin-engine/src/layout/mod.rs

Possible approaches

1. Run the incremental compiler against C-LEARN (and any other panicking models) under a debug build to capture the panic backtrace and identify the root cause
2. Convert the panic site(s) to return Result::Err with proper diagnostics
3. Once fixed, remove the catch_unwind wrappers in benchmarks and tests (layout/analysis catch_unwind may still be justified for defense-in-depth against malformed user models)

Context

Identified during review of the salsa consolidation branch (salsa-consolidation), where the benchmark and test code were updated to use the incremental path.