feat: Add SiblingSubgraph::from_node

[aborgna-q]

Complementary improvement to #1654.
Creating a k-node subgraph in an n-node graph should ideally be O(k).
However, due to CQCL/portgraph#155 this ends up being O(n).

For k=1, this results in a linear cost overhead.
This PR adds a special case (written by @doug-q) that completely skips the unnecessary checks.

group                         before                                 from_node
-----                         ------                                 ---------
multinode_subgraph/10         1.01     17.7±0.26µs        ? ?/sec    1.00     17.5±0.23µs        ? ?/sec
multinode_subgraph/100        1.00   169.1±11.34µs        ? ?/sec    1.00    168.8±4.37µs        ? ?/sec
multinode_subgraph/1000       1.01      2.3±0.46ms        ? ?/sec    1.00      2.3±0.34ms        ? ?/sec
singleton_subgraph/10         12.26     3.0±0.06µs        ? ?/sec    1.00   245.6±21.24ns        ? ?/sec
singleton_subgraph/100        20.01     4.7±0.06µs        ? ?/sec    1.00    234.4±6.50ns        ? ?/sec
singleton_subgraph/1000       93.34    22.0±0.25µs        ? ?/sec    1.00    235.6±4.93ns        ? ?/sec

[codecov]

Codecov Report

Attention: Patch coverage is 96.55172% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.52%. Comparing base (e63878f) to head (68d2a59).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-core/src/hugr/views/sibling_subgraph.rs	96.55%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1655   +/-   ##
=======================================
  Coverage   85.51%   85.52%           
=======================================
  Files         136      136           
  Lines       25264    25293   +29     
  Branches    22176    22205   +29     
=======================================
+ Hits        21605    21632   +27     
- Misses       2455     2456    +1     
- Partials     1204     1205    +1     

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python	92.42% <ø> (ø)
rust	84.56% <96.55%> (+0.01%)	⬆️

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[doug-q]

I think a better commit message here is feat: Add SiblingSubgraph::from_node.

[doug-q]

This change doesn't seem necessary. try_from_nodes_with_checker already does this, and TopoConvexChecker::new is cheap now.

[doug-q]

Nice.