Move predict from Turing, implemented using fix

[sunxd3]

fix #647

Turing's implementation relies on setval_and_resample! to generate the predictions, and use bundle_samples function implemented in Turing.Inference.

This PR provides a draft implementing predict using the new fix interface: given a sample from the posterior, we can fix the values of model parameters with the posterior sample, then just generate one sample from prior.

This doesn't work yet.

[coveralls]

Pull Request Test Coverage Report for Build 10715016218

Details

• 0 of 25 (0.0%) changed or added relevant lines in 1 file are covered.
• 19 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.5%) to 77.052%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
ext/DynamicPPLMCMCChainsExt.jl	0	25	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/model.jl	1	88.46%
src/threadsafe.jl	18	49.57%

Totals
Change from base Build 10701838580:	-0.5%
Covered Lines:	2713
Relevant Lines:	3521

---

💛 - Coveralls

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 22 lines in your changes missing coverage. Please review.

Project coverage is 74.77%. Comparing base (bf73fd0) to head (cb557e2).

Files with missing lines	Patch %	Lines
ext/DynamicPPLMCMCChainsExt.jl	0.00%	22 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #651      +/-   ##
==========================================
- Coverage   74.87%   74.77%   -0.10%     
==========================================
  Files          29       29              
  Lines        3260     3287      +27     
==========================================
+ Hits         2441     2458      +17     
- Misses        819      829      +10     

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