support elementwise add/sub of NormalRVs

[eclipse1605]

• Closes support measurable rewrites for pt.add and pt.sub of NormalRVs #8073
• Related to observe(sum) for Normal via rewrite to equivalent NormalRV #8067, ENH: pymc.math.sum could not be observed #7990

[codecov]

Codecov Report

❌ Patch coverage is 88.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.88%. Comparing base (c868a84) to head (ef13c34).

Files with missing lines	Patch %	Lines
pymc/logprob/arithmetic.py	88.33%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8074      +/-   ##
==========================================
- Coverage   90.89%   90.88%   -0.01%     
==========================================
  Files         123      123              
  Lines       19489    19547      +58     
==========================================
+ Hits        17714    17765      +51     
- Misses       1775     1782       +7     

Files with missing lines	Coverage Δ
pymc/logprob/arithmetic.py	91.86% <88.33%> (-8.14%)	⬇️

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[eclipse1605]

@ricardoV94 do we remove the failing test or change the name and make the replacement

res = conditional_logp({y_rv: y})
assert y in res

[ricardoV94]

@ricardoV94 do we remove the failing test or change the name and make the replacement

res = conditional_logp({y_rv: y})
assert y in res

change it to use other RVs that don't have closed form solution

[eclipse1605]

change it to use other RVs that don't have closed form solution

sure ill do

x_rv1 = pt.random.exponential(name="x_rv1")
x_rv2 = pt.random.exponential(name="x_rv2")

[eclipse1605]

@ricardoV94 the failing test if flaky right?

[ricardoV94]

change it to use other RVs that don't have closed form solution

sure ill do

x_rv1 = pt.random.exponential(name="x_rv1")
x_rv2 = pt.random.exponential(name="x_rv2")

that's equivalent to a gamma, use different scales in each rv, to be more future proof