Support `request.node`

[MatthewMckee4]

If the request is for a test function the request.node is just the current function.

Otherwise, from pytest:

    @property
    def node(self):
        scope = self._scope
        if scope is Scope.Function:
            # This might also be a non-function Item despite its attribute name.
            node: nodes.Node | None = self._pyfuncitem
        elif scope is Scope.Package:
            node = get_scope_package(self._pyfuncitem, self._fixturedef)
        else:
            node = get_scope_node(self._pyfuncitem, scope)
        if node is None and scope is Scope.Class:
            # Fallback to function item itself.
            node = self._pyfuncitem
        assert node, (
            f'Could not obtain a node for scope "{scope}" for function {self._pyfuncitem!r}'
        )
        return node