InitContext, part 2 - Move hasvalue and getvalue to AbstractPPL; enforce key type of AbstractDict

[penelopeysm]

Part 1: Adding hasvalue and getvalue to AbstractPPL

This is Part 2/N of splitting #967 up into manageable bits.

---

In Part 1 we defined the following methods in AbstractPPL:

hasvalue(::NamedTuple, ::VarName[, ::Distribution])
hasvalue(::AbstractDict{<:VarName}, ::VarName[, ::Distribution])
getvalue(::NamedTuple, ::VarName[, ::Distribution])
getvalue(::AbstractDict{<:VarName}, ::VarName[, ::Distribution])

This PR removes them (and their helper functions) from the DynamicPPL codebase.

In DynamicPPL, their type bounds for Dict arguments were too lax: they used to take AbstractDict{<:Any} as the first argument. The AbstractPPL versions have tighter bounds. This PR therefore switches all overly-loosely-typed Dicts to use a key type of VarName.

Closes #791

[github-actions]

Benchmark Report for Commit 21cf568

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 |                  8.2 |                 1.5 |
|           Smorgasbord |       201 | forwarddiff |             typed |  false |                663.4 |                39.1 |
|           Smorgasbord |       201 | forwarddiff | simple_namedtuple |   true |                421.9 |                49.2 |
|           Smorgasbord |       201 | forwarddiff |           untyped |   true |                977.4 |                36.4 |
|           Smorgasbord |       201 | forwarddiff |       simple_dict |   true |               6558.5 |                24.9 |
|           Smorgasbord |       201 | reversediff |             typed |   true |               1055.9 |                38.5 |
|           Smorgasbord |       201 |    mooncake |             typed |   true |               1027.4 |                 4.2 |
|    Loop univariate 1k |      1000 |    mooncake |             typed |   true |               6007.7 |                 3.9 |
|       Multivariate 1k |      1000 |    mooncake |             typed |   true |                993.5 |                 9.0 |
|   Loop univariate 10k |     10000 |    mooncake |             typed |   true |              67201.0 |                 3.5 |
|      Multivariate 10k |     10000 |    mooncake |             typed |   true |               8456.2 |                 9.9 |
|               Dynamic |        10 |    mooncake |             typed |   true |                133.8 |                12.9 |
|              Submodel |         1 |    mooncake |             typed |   true |                 12.7 |                 6.3 |
|                   LDA |        12 | reversediff |             typed |   true |               1452.1 |                 1.7 |

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.92%. Comparing base (2074657) to head (21cf568).

Additional details and impacted files

@@             Coverage Diff              @@
##           breaking     #980      +/-   ##
============================================
- Coverage     82.67%   81.92%   -0.75%     
============================================
  Files            38       37       -1     
  Lines          4022     3994      -28     
============================================
- Hits           3325     3272      -53     
- Misses          697      722      +25     

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[github-actions]

DynamicPPL.jl documentation for PR #980 is available at:
https://TuringLang.github.io/DynamicPPL.jl/previews/PR980/