Rename Deterministic vars Attribute To value

[AFg6K7h4fhy2]

As per DHM:

This will make it more consistent with SampledValue, and indeed allow for creating new DeterministicVariable instances by unpacking SampledValue instances (see #262 (comment))

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.80%. Comparing base (b11f270) to head (5fd7f22).

Files	Patch %	Lines
model/src/pyrenew/deterministic/deterministic.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #331   +/-   ##
=======================================
  Coverage   92.80%   92.80%           
=======================================
  Files          39       39           
  Lines         904      904           
=======================================
  Hits          839      839           
  Misses         65       65           

Flag	Coverage Δ
unittests	92.80% <90.90%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[damonbayer]

Thank @AFg6K7h4fhy2!