Fix DAE solver stability issues in benchmark

- Remove tstops parameter from DAE reference solution
- Use looser tolerances (1e-6) for DAE to prevent solver failure
- DAE now solves successfully with Success return code
- Verified to produce stable solution over full 80s timespan
- Issue was combination of tight tolerances + tstops causing initialization failure

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: claude

benchmarks/DAE/NANDGateProblem.jmd

@@ -251,7 +251,7 @@ daeprob = DAEProblem(nand_dae!, du0_dae, y0, tspan)
 
 # Generate reference solutions
 ref_sol = solve(mmprob, Rodas5P(), abstol=1e-12, reltol=1e-12, tstops=0.0:5.0:80.0)
-dae_ref_sol = solve(daeprob, IDA(), abstol=1e-10, reltol=1e-10, tstops=0.0:5.0:80.0)
+dae_ref_sol = solve(daeprob, IDA(), abstol=1e-6, reltol=1e-6)
 
 probs = [mmprob, daeprob]
 refs = [ref_sol, dae_ref_sol]