Allow (or test that) step functions can have the same name

[youtux]

We should allow (or make sure we test that) step functions can have the same name even within the same module and that multiple step decorators can be applied and work as expected.
This will allow all steps to be called _ (inspired by ward), since most of the context is given by the name= parameter passed to the step definition.

For example, this should be allowed, documented and tested.

@given(parsers.parse("there is a foo with value {value:d}"), target_fixture="foo")
@given(parsers.parse("there is a second with value {value}"), target_fixture="second_foo", converters={"value": int})
def _(value: int) -> Foo:
    return Foo(value=value)


@given("there is a bar", target_fixture="bar")
@given("there is a second bar", target_fixture="second_bar")
def _() -> Bar:
    return Bar()


@when("I click the foo")
def _(foo) -> None:
    return foo.click()


@when("I click the bar")
def _(bar) -> None:
    return bar.click()
...

Possibly replacing all the usages in the README.rst too.