Remove 3-argument {_,}evaluate!!; clean up submodel code

[penelopeysm]

This PR:

• removes the one last usage of evaluate!!(model, varinfo, context) in the DynamicPPL codebase
• removes _evaluate!!(model, varinfo, context) as this method was only being used for submodels

In return, it introduces:

• _evaluate!!(submodel, varinfo, context, left). Yes, yes, I basically moved the implementation from one place to the other; but the whole point is that this was special-case behaviour that was only needed for submodels, so this at least makes it clearer.

It also removes a lot of wrapper code for submodels. I personally don't see the need for more than one layer of indirection for submodels (in terms of the data structure, the only difference between a submodel and a model is that the submodel carries information about whether it should be auto-prefixed). I had mucked around with this in #815 and I didn't find any real problems with removing the wrappers there (in fact in that PR I went one step further and removed all wrappers, but that would have made it impossible to opt-out of prefixing and that's Bad(TM)).

I didn't add any new tests, but test/submodel.jl already contains quite extensive tests to make sure that everything behaves and it passes these tests so I'm quite happy.

#959 needs to be merged first. Done.

Follow-up from #952

Closes #720 (for good)

[github-actions]

Benchmark Report for Commit bfa48b3

Computer Information

Julia Version 1.11.5
Commit 760b2e5b739 (2025-04-14 06:53 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 |                  8.5 |                 1.6 |
|           Smorgasbord |       201 | forwarddiff |             typed |  false |                689.0 |                43.2 |
|           Smorgasbord |       201 | forwarddiff | simple_namedtuple |   true |                438.4 |                49.6 |
|           Smorgasbord |       201 | forwarddiff |           untyped |   true |               1181.9 |                30.1 |
|           Smorgasbord |       201 | forwarddiff |       simple_dict |   true |               6524.2 |                25.1 |
|           Smorgasbord |       201 | reversediff |             typed |   true |               1070.6 |                38.8 |
|           Smorgasbord |       201 |    mooncake |             typed |   true |               1043.1 |                 4.3 |
|    Loop univariate 1k |      1000 |    mooncake |             typed |   true |               6080.7 |                 3.9 |
|       Multivariate 1k |      1000 |    mooncake |             typed |   true |               1010.0 |                 9.1 |
|   Loop univariate 10k |     10000 |    mooncake |             typed |   true |              68325.8 |                 3.6 |
|      Multivariate 10k |     10000 |    mooncake |             typed |   true |               9028.8 |                 9.8 |
|               Dynamic |        10 |    mooncake |             typed |   true |                139.5 |                13.8 |
|              Submodel |         1 |    mooncake |             typed |   true |                 13.6 |                 6.1 |
|                   LDA |        12 | reversediff |             typed |   true |               1280.5 |                 2.6 |

[codecov]

Codecov Report

Attention: Patch coverage is 95.45455% with 1 line in your changes missing coverage. Please review.

Project coverage is 82.76%. Comparing base (7f20709) to head (bfa48b3).

Files with missing lines	Patch %	Lines
src/context_implementations.jl	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           breaking     #960      +/-   ##
============================================
- Coverage     82.85%   82.76%   -0.09%     
============================================
  Files            38       38              
  Lines          4031     4010      -21     
============================================
- Hits           3340     3319      -21     
  Misses          691      691              

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[github-actions]

DynamicPPL.jl documentation for PR #960 is available at:
https://TuringLang.github.io/DynamicPPL.jl/previews/PR960/