ADD: Harr wavelet example

[rcjackson]

This PR implements the Harr wavelet technique for retrieving PBL from lidar backscatter profiles. An example for the test ceilometer data is included. Co-authored by Claude Sonnet 5. This will add PyWavelets as an optional dependency.

References:

Brooks, I. M. (2003). Finding boundary layer top using
wavelet covariance transform. Journal of Atmospheric and Oceanic
Technology, 20(8), 1092-1105.
https://doi.org/10.1175/1520-0426(2003)20%3C1092:FBLTUB%3E2.0.CO;2

Cohn, S. A., & Angevine, W. M. (2000). Boundary layer height and
entrainment zone thickness measured by lidars and wind-profiling
radars. Journal of Applied Meteorology, 39(8), 1233-1247.
https://doi.org/10.1175/1520-0450(2000)039%3C1233:BLHAEZ%3E2.0.CO;2

• Closes #xxxx
• Tests added
• Documentation reflects changes
• PEP8 Standards or use of linter
• Xarray Dataset or DataArray variable naming follows 'ds' or 'da' naming

[zssherman]

@AdamTheisen Are you fine if we add a new optional dependency for this code?

[AdamTheisen]

@zssherman I think a new dependency like scipy is fine to bring in and likely something we would do in the long run anyways. I would want to finalized a decision on my question in #1040 before merging this one.

[zssherman]

We will have to fix conflicts here with the new merge of the other PR

[rcjackson]

@zssherman Strange, it seems to be trying to sandwich both routines together....

[zssherman]

@AdamTheisen Are you fine with us adding pywavelets as a dependency to the doc build CI? If approved @rcjackson we can add that in

[AdamTheisen]

@zssherman that's fine for the doc build. Are we treating this as an optional dependency for ACT in general?

[zssherman]

@AdamTheisen It is being treated as an optional dependency, I also mispoke, it would be added to both the doc build CI and the regular CI

[zssherman]

I updated the PR to add pywavelets to the doc build