Update NonStiffODE benchmarks for ModelingToolkit v10 compatibility

Updates the NonStiffODE benchmark suite to support ModelingToolkit v10 alongside v9:

**Changes:**
- Updated `benchmarks/NonStiffODE/Project.toml` to allow ModelingToolkit v9 and v10
- Removed IfElse.jl dependency (no longer supported in MTK v10)
- Removed `using IfElse` import from enright_pryce.jl
- Existing code already uses `Base.ifelse` through `myifelse` function (compatible)
- Existing ODESystem calls already specify independent variable (compatible)
- Existing code already uses `complete` for system finalization (compatible)

**Compatibility:**
- All existing ModelingToolkit usage patterns are already compatible with v10
- No breaking changes to benchmark behavior or results expected
- Maintains backward compatibility with MTK v9

This enables users to run NonStiffODE benchmarks with the latest ModelingToolkit
v10 while maintaining compatibility with existing v9 installations.

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

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

Author: ChrisRackauckas