Implement cftime vectorization as discussed in PR #8322

[antscloud]

As discussed in #8322, here is the test for implementing the vectorization

Only this test seems to fail in test_coding_times.py :

xarray/xarray/tests/test_coding_times.py

Lines 1061 to 1071 in f895dc1

	@requires_cftime
	@pytest.mark.parametrize("freq", ["U", "L", "S", "T", "H", "D"])
	def test_encode_decode_roundtrip_cftime(freq) -> None:
	initial_time = cftime_range("0001", periods=1)
	times = initial_time.append(
	cftime_range("0001", periods=2, freq=freq) + timedelta(days=291000 * 365)
	)
	variable = Variable(["time"], times)
	encoded = conventions.encode_cf_variable(variable)
	decoded = conventions.decode_cf_variable("time", encoded, use_cftime=True)
	assert_equal(variable, decoded)

I don't really understand why though if you have an idea

[kmuehlbauer]

@antscloud Nice catch! I have two suggestion to get the test suite running.

[headtr1ck]

@antscloud are you willing to continue this? It would be a good addition.

[antscloud]

Hi, sorry i completely forgot about this issue, i've implemented the suggestions and all the tests appear to pass, I hope it works in the CI 🤞

[headtr1ck]

BENCHMARKS NOT SIGNIFICANTLY CHANGED.

I didn't check in detail if we have a test that might cover this already and if yes, what the changes are.

[spencerkclark]

I don't think we currently do, but I think this new benchmark should cover it: #9262.

[spencerkclark]

Thanks @antscloud! I think this looks good to me now. Could you add a what's new entry under a new Performance heading?

[headtr1ck]

| Change | Before [91a52dc] | After [3512bee] | Ratio | Benchmark (Parameter) |
|----------|----------------------|---------------------|---------|-----------------------------------------------------------|
| - | 139±0.9ms | 42.3±0.7ms | 0.3 | coding.EncodeCFDatetime.time_encode_cf_datetime('noleap') |

3 times faster, not bad

[headtr1ck]

Looks good to me!

[headtr1ck]

mypy complains here.
Not sure if this is an issue of wrong typing of numpy, or if this is not a recommended way of calling equals. (I think the None is the problem).

[headtr1ck]

The mypy error is still there, not sure how to effectively fix it, maybe use kwargs instead or simply type ignore it.

Otherwise this looks good and should get an entry in whats-new!