CLN: de-privatize _parsers and _engines in pandas/core/computation and rename to something more descriptive

[hwalinga]

As a followup from #28215

_parsers and _engines as used in the code for the .query and .eval methods should be de-privatized and named to something more informative.

_engines: Dict[str, Type[AbstractEngine]] = {
    "numexpr": NumExprEngine,
    "python": PythonEngine,
}

_parsers = {"python": PythonExprVisitor, "pandas": PandasExprVisitor}

@jreback

[jbrockmendel]

theres are now ENGINES and PARSERS i think

[hwalinga]

Correct. Well I guess this can be closes then!

I also wouldn't think what a better name for those would be. I think only parser was a bit too generic term. Maybe ENGINE_PARSERS, AST_VISITOR?

ENGINES is probably good. What do you think?

[jbrockmendel]

These are pretty deeply internal, i wouldnt worry about it