avoid duplicate log statements by memoizing getters

[minrk]

ensures get_ functions are called only once, avoiding duplicate log statements. Closes #1246 .

This may be too clever to do it magically on methods that start with get_, but it works and is the simplest if we want to clearly always cache all these methods (I think we do).

The alternatives are:

1. more standard, far more changes (both now and over time) - apply @lru_cache() on every method, including every subclass method override (easy to miss, as the only downside of forgetting it is duplicate log statements and a negligible amount of wasted time)
2. to ensure these methods are called only once on the parent class, e.g. by assigning the results to variables, or calling directly via an additional private method self._get_.... This is ultimately the same as the memoize here, but implemented with explicit private methods instead of caching all public methods based on their name.
3. like 2., but only on the functions we expect to call more than once (get_..._files() are called in build and again in render)

[yuvipanda]

While this is super clever, this makes me somewhat uncomfortable - I can imagine myself up at 3am some day, looking for reasons why my get_somethingelse method is just not being called. I'd much prefer alternative 1, with lru being decorated for each of them...

[minrk]

Fair enough! Now @lru_cache is applied to all get methods explicitly

[yuvipanda]

Thanks @minrk