Fix ValueVariable checks

[brandonwillard]

This PR fixes a number of incorrect checks for ValueVariables. It also closes #240, makes updates according to recent Aesara deprecations, and adjusts the tests to use RandomStream (e.g. so that we don't miss out on the updates that would normally appear in such graphs).

[brandonwillard]

After these fixes/updates, test_transforms.test_transform_reused_measurable needed to be marked as xfail. Since that test is for a non-standard situation, we should merge this first and address that later.

[codecov]

Codecov Report

Patch coverage: 70.00% and project coverage change: -0.43 ⚠️

Comparison is base (5f5aaa4) 96.19% compared to head (f8f3afd) 95.76%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #242      +/-   ##
==========================================
- Coverage   96.19%   95.76%   -0.43%     
==========================================
  Files          12       12              
  Lines        1996     2006      +10     
  Branches      239      243       +4     
==========================================
+ Hits         1920     1921       +1     
- Misses         39       46       +7     
- Partials       37       39       +2     

Impacted Files	Coverage Δ
aeppl/censoring.py	96.15% <ø> (ø)
aeppl/cumsum.py	100.00% <ø> (ø)
aeppl/logprob.py	97.54% <ø> (-0.55%)	⬇️
aeppl/rewriting.py	95.91% <ø> (ø)
aeppl/scan.py	96.90% <ø> (ø)
aeppl/tensor.py	100.00% <ø> (ø)
aeppl/printing.py	90.23% <62.50%> (-1.54%)	⬇️
aeppl/dists.py	94.50% <100.00%> (ø)
aeppl/mixture.py	96.49% <100.00%> (ø)
aeppl/transforms.py	96.68% <100.00%> (-0.26%)	⬇️

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