InitContext, part 5 - Remove SamplingContext, SampleFrom{Prior,Uniform}, {tilde_,}assume

[penelopeysm]

Part 1: Adding hasvalue and getvalue to AbstractPPL
Part 2: Removing hasvalue and getvalue from DynamicPPL
Part 3: Introducing InitContext and init!!
Part 4: Using InitFromParams to implement predict, returned, and initialize_values

This is part 5/N of #967.

This PR removes everything that is no longer needed. SamplingContext, SampleFromPrior, SampleFromUniform, now have direct one-to-one replacements (albeit with slightly different behaviour since they now always overwrite variables in the varinfo).

It also removes assume and tilde_assume.

Prior to this PR we had two different kinds of assume, one with a sampler and one without. Now we only have the one without, so we can just move that definition into tilde_assume!!(::DefaultContext, ...).

Finally, tilde_assume has been subsumed into tilde_assume!! as we can just dispatch on the type of right. (Previously this wasn't possible because there was a lot of stuff about is_rhs_model, etc. etc. which was removed in #960.)

Closes #859
Closes #955

[github-actions]

Benchmark Report for Commit 8e3dcac

Computer Information

Julia Version 1.11.6
Commit 9615af0f269 (2025-07-09 12:58 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 4 × AMD EPYC 7763 64-Core Processor
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, znver3)
Threads: 1 default, 0 interactive, 1 GC (on 4 virtual cores)

Benchmark Results

|                 Model | Dimension |  AD Backend |      VarInfo Type | Linked | Eval Time / Ref Time | AD Time / Eval Time |
|-----------------------|-----------|-------------|-------------------|--------|----------------------|---------------------|
| Simple assume observe |         1 | forwarddiff |             typed |  false |                  8.4 |                 1.6 |
|           Smorgasbord |       201 | forwarddiff |             typed |  false |                630.8 |                41.9 |
|           Smorgasbord |       201 | forwarddiff | simple_namedtuple |   true |                402.0 |                54.6 |
|           Smorgasbord |       201 | forwarddiff |           untyped |   true |               1094.5 |                29.7 |
|           Smorgasbord |       201 | forwarddiff |       simple_dict |   true |               6369.2 |                28.2 |
|           Smorgasbord |       201 | reversediff |             typed |   true |               1009.1 |                40.3 |
|           Smorgasbord |       201 |    mooncake |             typed |   true |                960.3 |                 4.2 |
|    Loop univariate 1k |      1000 |    mooncake |             typed |   true |               5577.2 |                 3.9 |
|       Multivariate 1k |      1000 |    mooncake |             typed |   true |                950.4 |                 9.1 |
|   Loop univariate 10k |     10000 |    mooncake |             typed |   true |              62727.0 |                 3.5 |
|      Multivariate 10k |     10000 |    mooncake |             typed |   true |               8418.4 |                 9.9 |
|               Dynamic |        10 |    mooncake |             typed |   true |                126.9 |                12.0 |
|              Submodel |         1 |    mooncake |             typed |   true |                 12.7 |                 4.7 |
|                   LDA |        12 | reversediff |             typed |   true |               1195.9 |                 2.8 |

[codecov]

Codecov Report

❌ Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.46%. Comparing base (23cafe0) to head (331279c).

Files with missing lines	Patch %	Lines
src/context_implementations.jl	86.66%	2 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##           py/actually-use-init     #985      +/-   ##
========================================================
+ Coverage                 80.57%   81.46%   +0.89%     
========================================================
  Files                        39       39              
  Lines                      3927     3825     -102     
========================================================
- Hits                       3164     3116      -48     
+ Misses                      763      709      -54     

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[github-actions]

DynamicPPL.jl documentation for PR #985 is available at:
https://TuringLang.github.io/DynamicPPL.jl/previews/PR985/

[penelopeysm]

I couldn't find a way to reproduce this test without SamplingContext and the whole tilde-pipeline machinery that this PR removes, so I think that this is no longer relevant.