Possible replacement for Unitful

A possible replacement for [Unitful.jl](https://github.com/PainterQubits/Unitful.jl) is [UDUnits.jl](https://github.com/Alexander-Barth/UDUnits.jl).

Compared to Unitful.jl, the pros for using UDUnits.jl are

1. In place conversion via `Converter` function.
2. Support expressions like `W m^2` (although, it doesn't support `W * m^2`, but this can easily be fixed by parsing the expression beforehand and I don't think any of the diagnostics write units like this)
3. Should be compatible with NetCDF files outside of CliMA since "the values of the units attributes [of NetCDF files] are character strings that are recognized by UNIDATA’s UDUNITS package..." in section 3.1 of the CF Conventions. Note that the UNIDATA’s UDUNITS package is a C library and UDUnits.jl is a Julia interface for the package.
4. Support units that we care about like `degree_east` and is generally more flexible with what units it can parse. For example, `s`, `sec`, `secs`, `second`, and `seconds` are all recognizable by UDUnits.jl and only `s` is recognizable by Unitful.jl. For another example, `m**2` (Python syntax) is parseable by UDUnits.jl, but is not by Unitful.jl.
5. Less dependencies. See Project.toml of [Unitful.jl](https://github.com/PainterQubits/Unitful.jl/blob/master/Project.toml) and [UDUnits.jl](https://github.com/Alexander-Barth/UDUnits.jl/blob/master/Project.toml) respectively.

The cons for using UDUnits.jl are

1. Not as popular as Unitful.jl, so there may be potential bugs that have not been discovered.
2. Doesn't support conversion of non-Float64 numbers (probably a bug).

Start by comparing the Unitful.jl and UDUnits.jl links in the issue, focusing on conversion behavior, supported unit syntax, numeric types, dependencies, and NetCDF compatibility. Done would require a project decision and an agreed implementation scope for replacing Unitful.jl; no repository files or tests are identified.

Written by the indexing model from the issue text.