Speedup: Single-precision hilbert, resample, and lfilter_zi.

[luigifcruz]

Hi!

I noticed some functions weren't respecting the input type and thus returning double precision results.

This pull request proposes two changes:

1. Make resample return a buffer with the same dtype as input.
2. Add single-precision hilbert and hilbert2 kernels.

I also benchmarked each change:

1. Upstream: 471 µs vs. Proposed: 260 µs
2. Upstream: 1.47 ms vs. Proposed: 610 µs

[mnicely]

Hi @luigifcruz
Good catch on data type.
I'll get back to you soon with a review, I think there might be a simpler solution.

[mnicely]

Can you please type specific tests as well, in test_filtering.py

    @pytest.mark.benchmark(group="Hilbert")
    @pytest.mark.parametrize("dtype", [np.float32, np.float64])
    @pytest.mark.parametrize("dim, num_samps", [(1, 2 ** 15), (2, 2 ** 8)])
    class TestHilbert:
...

[awthomp]

Thanks for the PR @luigifcruz! Once you make these suggested changes from @mnicely, we'll merge. I changed the merge target branch to branch-22.02 instead of main and added some CI flags to get all checks to clear. I still think we'll have a style change, but Matt may have pointed that out too.

[ajschmidt8]

Approving ops-codeowner file changes

[luigifcruz]

Thanks for the feedback @mnicely & @awthomp!

I implemented the requested style changes with 9d6d7aa and type check tests with bc9dcd9. I had to patch the linspace_data_gen function to accept a optional dtype argument with 279fe01. I also had to increase the tolerances of the array_equal method for single-precision arrays with 7ea86f6. This patch is required to successfully pass all tests. I believe this is caused by Scipy using double-precision arrays. I submitted a PR to Scipy but the fix should be available only with scipy>=1.9.0. You guys might want to handle the tolerances in a different way than I implemented.

I also noticed that the lfilter_zi method was returning a double-precision array no matter the input type. This would result in the filtfilt method always retuning a double-precision value. The patches for this are found in b5000ef.

[awthomp]

@mnicely -- I don't think we can merge until you sign off on @luigifcruz 's fixes. Can you give this a look?

Looks great, Luigi. You're the best! Thanks, as always, for contributing.

[awthomp]

@gpucibot merge

[luigifcruz]

Awesome, @awthomp! Thanks all for maintaining this awesome project!