BUG: EWM.__getitem__ raised error with times

[mroeschke]

• tests added / passed
• Ensure all linting tests pass, see here for how to run them
• whatsnew entry

Also somewhat ameliorates the performance hit in #40072 (comment)

dtype="float"
window=1000
N = 10 ** 5
arr = (100 * np.random.random(N)).astype(dtype)
ewm = pd.Series(arr).ewm(halflife=window)

%timeit ewm.mean()
# Master
2.59 ms ± 25.5 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

# PR
2.5 ms ± 31.5 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

[jreback]

does this address #40099?

[mroeschke]

does this address #40099?

No, that issue has the expected output given the formula we're using but needs a discussion whether we want to make an exception in that case

[jreback]

thanks @mroeschke