QA: make implicit imports explicit (ExplicitImports no_implicit_imports)

[ChrisRackauckas-Claude]

The QA group now runs ExplicitImports.jl's six checks via SciMLTesting run_qa(...; explicit_imports = true). Five pass. check_no_implicit_imports is currently tracked as ei_broken = (:no_implicit_imports,) because the module pulls many names implicitly from heavy using of ModelingToolkit / ParserCombinator / PythonCall / MLStyle / CondaPkg, and making them explicit is a larger refactor.

check_no_implicit_imports(BaseModelica) reports these implicit imports to convert to explicit using X: name (or qualified access):

From MLStyle: MLStyle, @data (MLStyle.DataType), @match (MLStyle.MatchImpl)
From CondaPkg: CondaPkg
From ModelingToolkit: ModelingToolkit, SymbolicUtils
From ModelingToolkitBase: ModelingToolkitBase, @discretes, @named, @parameters, System, equations, mtkcompile
From Symbolics: Symbolics, @variables, Equation, Num
From SciMLBase: ODEProblem
From SymbolicUtils: substitute
From ParserCombinator: ParserCombinator, @E_str, @e_str, @p_str, @with_names, Debug, Delayed, Drop, Lookahead, NoCache, Not, Plus, Space, Star, make, once
From PythonCall: PythonCall, Py, pybuiltins, pyconvert, pyimport

Once these are made explicit, drop :no_implicit_imports from ei_broken in test/qa/qa.jl (the @test_broken will Unexpected-Pass to prompt it).

Tracked as part of the SciMLTesting run_qa v1.6 / ExplicitImports rollout.