feat(rewrite): show a method call on one line

[RonnyPfannschmidt]

Stacked on #14816 → #14815 → #14814 → #14447 → #14921 → #14813. Its diff includes theirs.

obj.method() reported the bound method as an intermediate of its own:

where 42 = compute()
  where compute = Obj().compute

which spends a line on something nobody asked about. Build the explanation from the receiver and the attribute name instead:

where 42 = Obj().compute()

The bound method keeps its own temporary even though it no longer has its own explanation, because Python looks it up before evaluating the arguments. Inlining the attribute into the rewritten call — which is what the obvious implementation does — moves the lookup after the arguments, and with it the read of the receiver. That version fails two guards:

• test_method_receiver_in_order, a guard already in test(rewrite): systematic coverage matrix for assertion rewriting #14813 — assert obj.take(identity(obj := None)) raises AttributeError on None
• test_method_lookup_precedes_arguments, added here — a property-based bound method is looked up after the arguments run

I wrote it the inline way first and the guards caught it, which is the whole argument for landing the matrix ahead of the visitors.

testing/python/raises_group.py::test_assert_matches asserts on an exact rewritten message and is updated for the flat format.

Lands the introspect-method-call-flat cases of the coverage matrix in #14813 as passing tests, plus the new lookup-order guard above (+6).

Supersedes part of #14448.