Specialize on operations

[charleskawczynski]

This makes the following pattern easier:

∑tendencies = lazy.(∑tendencies .+ viscous_sponge_tendency_uₕ(ᶜuₕ, viscous_sponge)) as the result will return ∑tendencies directly. We can't easily broadcast on ∑tendencies if it's initialized with a scalar number.

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 34.21%. Comparing base (0523c23) to head (d59da43).

Files with missing lines	Patch %	Lines
src/NullBroadcasts.jl	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #6      +/-   ##
==========================================
- Coverage   36.11%   34.21%   -1.91%     
==========================================
  Files           1        1              
  Lines          36       38       +2     
==========================================
  Hits           13       13              
- Misses         23       25       +2     

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[charleskawczynski]

I really don't like this solution. The output type now depends on whether we write a .- (::NullBroadcasted) vs (::NullBroadcasted) .- a, which just seems bad. I think I'd rather do something more explicit, clunky and simple upstream.