Support as_int on bool series

[rebkwok]

Fixes #1313

• support using is_int on a bool series
• add spec test
• Update trino engine (has its own custom cast_to_int method to round floats towards zero, which isn't applicable for booleans)
• Replace the case statement for casting bools to ints in the measures framework

[madwort]

Code looks good, although because it's so end-user focused I'd like to see some more documentation - e.g. it should definitely be mentioned in https://docs.opensafely.org/ehrql/reference/features/#7-operations-on-boolean-series & maybe also as an alternative option in https://docs.opensafely.org/ehrql/reference/features/#1113-case-with-boolean-column ?

[rebkwok]

Code looks good, although because it's so end-user focused I'd like to see some more documentation - e.g. it should definitely be mentioned in https://docs.opensafely.org/ehrql/reference/features/#7-operations-on-boolean-series & maybe also as an alternative option in https://docs.opensafely.org/ehrql/reference/features/#1113-case-with-boolean-column ?

Thanks, I'd forgotten to add the new spec test file to the toc.py so the reference docs weren't being pulled in. Also added a comment in the case spec test.

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[madwort]

wow, not sure I'd really seen that test/docs tooling, that's brill (& the docs look much better now thanks)

[evansd]

Great, thanks for doing this!

One other thing it might be worth doing (non-urgently) is extending this bit of the generative tests so it produces examples of bools being cast to ints:

ehrql/tests/generative/variable_strategies.py

Lines 290 to 293 in b4adab2

	@st.composite
	def cast_to_int(draw, type_, frame):
	type_ = draw(any_numeric_type())
	return Function.CastToInt(draw(series(type_, frame)))

We've got code in the tests which will moan at you if you add a completely new operation and don't include it in the generative tests. But we don't have anything which reminds you to update the tests if you extend an existing operation (I don't quite know how we'd do that to be honest) so it's one of those things which we inevitably forget.

[evansd]

You could save eight whole characters by writing this as:

Series[Numeric | bool]

Eight, Becky! What were you thinking?