Add AbstractRNG types to fix method ambiguities in Turing

[penelopeysm]

Related to TuringLang/Turing.jl#2290

This PR fixes 4 of the following method ambiguities (which arise when testing Turing, but are probably better resolved here):

Ambiguity #1
dot_tilde_assume(rng, context::AbstractPPL.AbstractContext, args...) @ DynamicPPL ~/ppl/dppl/src/context_implementations.jl:294
dot_tilde_assume(context::Turing.Experimental.GibbsContext, right, left, vns, vi) @ Turing.Experimental ~/ppl/lib/src/experimental/gibbs.jl:77

Possible fix, define
  dot_tilde_assume(::Turing.Experimental.GibbsContext, ::AbstractPPL.AbstractContext, ::Any, ::Any, ::Any)

Ambiguity #2
dot_tilde_assume(rng, context::AbstractPPL.AbstractContext, args...) @ DynamicPPL ~/ppl/dppl/src/context_implementations.jl:294
dot_tilde_assume(ctx::Turing.Optimisation.OptimizationContext, right, left, vns, vi) @ Turing.Optimisation ~/ppl/lib/src/optimisation/Optimisation.jl:85

Possible fix, define
  dot_tilde_assume(::Turing.Optimisation.OptimizationContext, ::AbstractPPL.AbstractContext, ::Any, ::Any, ::Any)

Ambiguity #3
tilde_assume(rng, context::AbstractPPL.AbstractContext, args...) @ DynamicPPL ~/ppl/dppl/src/context_implementations.jl:66
tilde_assume(context::Turing.Experimental.GibbsContext, right, vn, vi) @ Turing.Experimental ~/ppl/lib/src/experimental/gibbs.jl:36

Possible fix, define
  tilde_assume(::Turing.Experimental.GibbsContext, ::AbstractPPL.AbstractContext, ::Any, ::Any)

Ambiguity #4
tilde_assume(rng, context::AbstractPPL.AbstractContext, args...) @ DynamicPPL ~/ppl/dppl/src/context_implementations.jl:66
tilde_assume(ctx::Turing.Optimisation.OptimizationContext, dist, vn, vi) @ Turing.Optimisation ~/ppl/lib/src/optimisation/Optimisation.jl:67

Possible fix, define
  tilde_assume(::Turing.Optimisation.OptimizationContext, ::AbstractPPL.AbstractContext, ::Any, ::Any)

[coveralls]

Pull Request Test Coverage Report for Build 10265975510

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 81.36%

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Files with Coverage Reduction	New Missed Lines	%
src/selector.jl	1	85.71%

Totals
Change from base Build 10061220559:	-0.03%
Covered Lines:	2811
Relevant Lines:	3455

---

💛 - Coveralls

[yebai]

@penelopeysm, feel free to modify the version and make a new release so TuringLang/Turing.jl#2290 can use the new version.

[sunxd3]

For ref: https://github.com/JuliaRegistries/Registrator.jl

[penelopeysm]

Will do now, thanks for the pointers! 🙂