feat: Replace Tuple with unary sums

[aborgna-q]

Closes #864.

Updates the Display impl of Sum as part of this change, so

graph LR
    subgraph 0 ["(0) CFG"]
        direction LR
        subgraph 2 ["(2) DataflowBlock"]
            direction LR
            3["(3) Input"]
            3--"0:0<br>usize"-->5
            4["(4) Output"]
            5["(5) Tag"]
            5--"0:0<br>Sum(General([TypeRow { types: [Type(Extension(CustomType { extension: IdentList(#quot;prelude#quot;), id: #quot;usize#quot;, args: [], bound: Eq }), Eq)] }, TypeRow { types: [Type(Extension(CustomType { extension: IdentList(#quot;prelude#quot;), id: #quot;usize#quot;, args: [], bound: Eq }), Eq)] }]))"-->4
        end
        2-."0:0".->6
        2-."1:0".->1
        1["(1) ExitBlock"]
        subgraph 6 ["(6) DataflowBlock"]
            direction LR
            7["(7) Input"]
            7--"0:1<br>usize"-->8
            8["(8) Output"]
            9["(9) const:sum:{tag:0, vals:[]}"]
            9--"0:0<br>Sum(UnitSum(1))"-->10
            10["(10) LoadConstant"]
            10--"0:0<br>Sum(UnitSum(1))"-->8
        end
        6-."0:0".->1
    end

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is now rendered as

graph LR
    subgraph 0 ["(0) CFG"]
        direction LR
        subgraph 2 ["(2) DataflowBlock"]
            direction LR
            3["(3) Input"]
            3--"0:0<br>usize"-->5
            4["(4) Output"]
            5["(5) Tag"]
            5--"0:0<br>[usize]+[usize]"-->4
        end
        2-."0:0".->6
        2-."1:0".->1
        1["(1) ExitBlock"]
        subgraph 6 ["(6) DataflowBlock"]
            direction LR
            7["(7) Input"]
            7--"0:1<br>usize"-->8
            8["(8) Output"]
            9["(9) const:sum:{tag:0, vals:[]}"]
            9--"0:0<br>[]"-->10
            10["(10) LoadConstant"]
            10--"0:0<br>[]"-->8
        end
        6-."0:0".->1
    end

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And tuples appear directly as [usize, usize, ...].
We were incorrectly using the debug formatter for the internal types.

drive-by: Add rust snapshots to the pre-commit ignores. We don't want it to modify whitespaces.

[codecov]

Codecov Report

Attention: Patch coverage is 94.11765% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 85.68%. Comparing base (63afb03) to head (cfe31e2).

Files	Patch %	Lines
quantinuum-hugr/src/types.rs	94.11%	1 Missing ⚠️
quantinuum-hugr/src/utils.rs	92.30%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #891      +/-   ##
==========================================
+ Coverage   85.55%   85.68%   +0.12%     
==========================================
  Files          78       78              
  Lines       14396    14417      +21     
  Branches    14396    14417      +21     
==========================================
+ Hits        12317    12353      +36     
+ Misses       1445     1430      -15     
  Partials      634      634              

Flag	Coverage Δ
python	∅ <ø> (∅)
rust	85.68% <94.11%> (+0.12%)	⬆️

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[aborgna-q]

This is the implementation side of the change, I'll update the spec too.

Edit: done

[aborgna-q]

We could also add an explicit single-element variant to SumType to optimize for tuples internally (this would be transparent to the user, as the current Unit|General variants).

[cqc-alec]

LGTM