feat(aot): graceful fallback to JIT when AOT compile fails

[cennn]

Problem

When MAGI_COMPILE_AOT=1 is set globally, models using SimpleFSDP/DTensor fail AOT compilation with:

Attempted to read undefined local variable
File ".../simple_fsdp/builder.py", line 236, in forward
    state.aot_compile(*args, **kwargs)
File ".../aot_compile.py", line 143, in aot_compile_fullgraph
    raise e.with_traceback(None) from e.__cause__

This crashes the entire warmup process, preventing AOT from being used even for compatible models (e.g., VAE which has no FSDP).

Solution

Catch exceptions in the AOT compile path and gracefully fall back to the JIT bytecode capture path. This allows MAGI_COMPILE_AOT=1 to be set globally:

• VAE (no FSDP): AOT compiles successfully → skip Dynamo trace on verify (~14s savings)
• Base/SR (SimpleFSDP+DTensor): AOT fails → falls back to JIT → inductor cache hits from bake tar

Key implementation details:

1. Catch any exception from state.aot_compile()
2. Reset compile_config.aot = False to prevent further AOT attempts for this state
3. Reset compiled_entry and call torch._dynamo.reset() to clear AOT-only guard_filter_fn
4. Re-run _ensure_compiled() for JIT mode and proceed with bytecode capture

Context

Part of CI cold-start optimization effort (athena PR #1112). AOT serializes Dynamo FX graphs so verify can skip Dynamo tracing + RestartAnalysis entirely (~42s savings for compatible models).

[cennn]

Superseded by #89 (rebased the still-useful parts onto current main). Closing this PR.