Fix deprecation warnings

[ChrisRackauckas-Claude]

Summary

• Remove __precompile__() call (no-op since Julia 1.8, modules precompile by default)
• Replace removed warn() function calls with @warn macro in dict_build.jl (warn was removed from Base in Julia 1.0)
• Fix build_param_list returning undefined variable param_dict instead of param_list
• Fix typo "my be" → "may be" in warning message
• Remove commented-out dead code using deprecated lufact() API (old Jacobian LU factorization code that used SymEngine.Basic)

Details

While no deprecation warnings are currently emitted at runtime (tests pass with --depwarn=error), the codebase contained usage of APIs that have been removed from Julia:

1. warn() function (removed in Julia 1.0, replaced by @warn macro): Used in build_indvar_dict and build_param_list in dict_build.jl. These code paths would cause UndefVarError if reached.

2. __precompile__(): Deprecated since Julia 1.8. All modules precompile by default now.

3. build_param_list bug: The function returned param_dict (undefined) instead of param_list. This function is currently unused but was broken.

4. Commented-out code with lufact(): Dead code from the SymEngine era using lufact() (renamed to lu in Julia 1.0) and Matrix{SymEngine.Basic}.

Upstream dependencies note

No upstream dependency changes needed. All current MTK v11 APIs used (tosymbol, generate_rhs, generate_tgrad, generate_jacobian, generate_factorized_W, System) work without deprecation warnings.

The test_undefined_exports Aqua test remains broken = true due to MTK v11 exporting Variable and find_solvables! which are undefined — this is an upstream MTK issue.

Test plan

• Tests pass with julia --depwarn=error (direct invocation)
• Tests pass with Pkg.test()
• Runic formatting check passes

🤖 Generated with Claude Code