feat: Add custom node labels in mermaid_string

[lmondada]

To move PersistentHugr out of hugr-core, I need to be able to provide custom node labels to the mermaid printer. Whilst adding a field for this to RenderConfig would not be breaking, the problem is that such a field would have to be an Option<HashMap>, which is non-Copy and non-Hash. That would be a breaking change to RenderConfig.

I have found a creative way around this here, keeping the Copy-able RenderConfig and adding a FullRenderConfig struct with support for From and TryInto.

Is this the preferred approach? How would I make a note that this ought to be simplified ahead of the next breaking release?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 78.02691% with 49 lines in your changes missing coverage. Please review.

Project coverage is 82.35%. Comparing base (1ecd755) to head (3c92e64). Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-core/src/hugr/views/render.rs	84.66%	24 Missing and 1 partial :warning:
hugr-core/src/hugr/persistent/trait_impls.rs	41.66%	14 Missing :warning:
hugr-core/src/hugr/views.rs	59.09%	9 Missing :warning:
hugr-core/src/hugr/persistent/parents_view.rs	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2275      +/-   ##
==========================================
+ Coverage   82.33%   82.35%   +0.01%     
==========================================
  Files         240      240              
  Lines       43577    43726     +149     
  Branches    39488    39637     +149     
==========================================
+ Hits        35881    36012     +131     
- Misses       5701     5719      +18     
  Partials     1995     1995              

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rust	82.04% <78.02%> (+0.02%)	:arrow_up:

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[ss2165]

How about replicating the MermaidFormatter builder pattern from Portgraph, just wrapping it with HUGR types? Existing methods would just build and finish this new struct internally, and you are free to add a with_node_style(Fn(Node) -> String) method to it.

Existing mermaid_string_with_config could be deprecated in favour of hugr.mermaid_formatter().with_config(..)

[lmondada]

@ss2165 this should be ready to be reviewed now! See if this is what you had in mind. Once this is merged in, you can also merge in https://github.com/CQCL/hugr/pull/2277. Thanks a lot!