refactor: RFC: remove helpers (post-RPITIT TLC)

[acl-cqc]

We don't really need the various helpers typed as returning NodeConnections etc. now, but removing them is a bit of a PITA because some of these structs contain each other (hence, must be parametrized) - so I haven't done all of them, thought I'd RFC first...

Note: rebased to come after #188

[acl-cqc]

The line count would look significantly better if the old, delegate!, versions of these didn't exceed the line length limit !!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.49%. Comparing base (c019771) to head (30f998e).

Additional details and impacted files

@@                Coverage Diff                 @@
##           acl/port_links     #181      +/-   ##
==================================================
- Coverage           83.54%   83.49%   -0.06%     
==================================================
  Files                  24       24              
  Lines                6315     6320       +5     
  Branches             6315     6320       +5     
==================================================
+ Hits                 5276     5277       +1     
- Misses                967      969       +2     
- Partials               72       74       +2     

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[codspeed-hq]

CodSpeed Performance Report

Merging #181 will not alter performance

_{Comparing acl/rm_helpers (30f998e) with acl/port_links (c019771)}

Summary

✅ 36 untouched benchmarks

[hugrbot]

This PR contains breaking changes to the public Rust API.
Please deprecate the old API instead (if possible), or mark the PR with a ! to indicate a breaking change.

cargo-semver-checks summary

--- failure trait_requires_more_generic_type_params: trait now requires more generic type parameters ---

Description:
A trait now requires more generic type parameters than it used to. Uses of this trait that supplied the previously-required number of generic types will be broken. To fix this, consider supplying default values for newly-added generic types.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-new-parameter-no-default
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.39.0/src/lints/trait_requires_more_generic_type_params.ron

Failed in:
trait NodeConnections (0 -> 1 required generic types) in /home/runner/work/portgraph/portgraph/PR_BRANCH/src/multiportgraph/iter.rs:276

--- failure type_requires_more_generic_type_params: type now requires more generic type parameters ---

Description:
A type now requires more generic type parameters than it used to. Uses of this type that supplied the previously-required number of generic types will be broken. To fix this, consider supplying default values for newly-added generic types.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-new-parameter-no-default
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.39.0/src/lints/type_requires_more_generic_type_params.ron

Failed in:
Struct NodeConnections (0 -> 1 required generic types) in /home/runner/work/portgraph/portgraph/PR_BRANCH/src/multiportgraph/iter.rs:276