feat: Cleanup Display of types and arguments

[aborgna-q]

Updates the Display implementation of poly functions, functions, types, type arguments, and type params so its easier to read.

Comparison below. I added the newlines manually.

Before:

forall Any _0.map(|i|i.to_string()).unwrap_or("-".to_string()).
    [array([
        Variable { v: TypeArgVariable { idx: 1, cached_decl: BoundedNat { bound: UpperBound(None) } } },
        Type { ty: TypeBase(Sum(General { rows: [TypeRowBase { types: [] }, TypeRowBase { types: [TypeBase(Variable(0, Any), Any)] }] }), Any) }
    ])]
 -> [[]][[
    array([
            Variable { v: TypeArgVariable { idx: 1, cached_decl: BoundedNat { bound: UpperBound(None) } } },
            Type { ty: TypeBase(Sum(General { rows: [TypeRowBase { types: [] }, TypeRowBase { types: [TypeBase(Variable(0, Any), Any)] }] }), Any) }
        ]),
        int([BoundedNat { n: 6 }])
    ]]

(yes, that is some hardcoded rust source)

After:

∀ (var#0 : Type) (var#1 : Nat). [array(var#1, Type([]+[var#0]))]
                             -> [[array(var#1, Type([]+[var#0])), int(6)]]

That is, a generic function on a type var and an unbounded natural that takes an array of (nat, option type) and returns a tuple with the array and an int.

It may be better if the tuple display used () instead of [], but that can be discussed later.

Update after review suggestions:

∀ (#0 : Type) (#1 : Nat). [array(#1, []+[#0])] -> [[array(#1, []+[#0]), int(6)]]

[aborgna-q]

I could also remove the var part of the variables, and just call them #42 (and/or use some other reserved character)

[codecov]

Codecov Report

Attention: Patch coverage is 27.27273% with 16 lines in your changes missing coverage. Please review.

Project coverage is 86.58%. Comparing base (8a3d98e) to head (89dbae0).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-core/src/types/poly_func.rs	22.22%	7 Missing ⚠️
hugr-core/src/types/custom.rs	33.33%	0 Missing and 4 partials ⚠️
hugr-core/src/types/signature.rs	25.00%	1 Missing and 2 partials ⚠️
hugr-core/src/types/type_param.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1802      +/-   ##
==========================================
- Coverage   86.59%   86.58%   -0.02%     
==========================================
  Files         188      188              
  Lines       34227    34234       +7     
  Branches    31098    31105       +7     
==========================================
  Hits        29640    29640              
- Misses       2900     2906       +6     
- Partials     1687     1688       +1     

Flag	Coverage Δ
python	92.58% <ø> (ø)
rust	85.97% <27.27%> (-0.02%)	⬇️

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[mark-koch]

Very nice, this is a lot more readable!

[mark-koch]

I'd prefer to get rid of the var part

[mark-koch]

Or just {ty}?