fixed minor issues

[shravanngoswamii]

also fix these in this pr:

1. • [ ] Found one more VI Assertion error: https://github.com/shravanngoswamii/TuringTutorials/blob/f89f0bc3680d1148dccc28992726e97a60affa83/tutorials/09-variational-inference/index.qmd#L154C1-L162C4

     • Error:

       AssertionError: Mean of m (VI posterior, 1000 samples): 0.0038075909149039334
       Stacktrace:
       [1] top-level scope
        @ ~/work/TuringTutorials/TuringTutorials/tutorials/09-variational-inference/index.qmd:160

2. • [x] @yebai Should I change this diagram to Graphviz: https://turinglang.org/TuringTutorials/tutorials/docs-04-for-developers-abstractmcmc-turing/#states

     Old Image Diagram	New with Mermaid Code

     ```{mermaid}
     graph TD
       spl["spl<br/>Sampler<br/>&lt;:AbstractSampler"]:::leftAlign
       state["spl.state<br/>State<br/>&lt;:AbstractSamplerState"]:::leftAlign
       alg["spl.alg<br/>Algorithm<br/>&lt;:InferenceAlgorithm"]:::leftAlign
       vi["spl.state.vi<br/>VarInfo<br/>&lt;:AbstractVarInfo"]:::leftAlign
       placeholder1["..."]:::placeholder
       placeholder2["..."]:::placeholder
       placeholder3["..."]:::placeholder
       placeholder4["..."]:::placeholder
     
       spl --> state
       spl --> alg
       spl --> placeholder1
     
       state --> vi
       state --> placeholder2
     
       alg --> placeholder3
       placeholder1 --> placeholder4
     
       classDef leftAlign text-align:left;
       classDef placeholder width:100px;

[yebai]

@yebai Should I change this diagram to Graphviz: https://turinglang.org/TuringTutorials/tutorials/docs-04-for-developers-abstractmcmc-turing/#states

Both Mermaid and GraphViz work; one possible advantage of GraphViz is that it supports Quarto's tex workflow, which we might do later.

[shravanngoswamii]

@yebai Should I change this diagram to Graphviz: https://turinglang.org/TuringTutorials/tutorials/docs-04-for-developers-abstractmcmc-turing/#states

Both Mermaid and GraphViz work; one possible advantage of GraphViz is that it supports Quarto's tex workflow, which we might do later.

I converted it to Graphviz too:

[shravanngoswamii]

I can add whatever you prefer!

[shravanngoswamii]

@yebai If visibility of that assertion error is not an issue than this PR is good to go