fix: NodeMeta and PortMeta should be generic

[aborgna-q]

Fixes #282.

We partially implemented generic node/port/portOffset parameters for some portgraph containers, but NodeMeta and PortMeta still were stuck hardcoding the types.

This change ensures everything is generic.

• I had to add a Unsigned::NonZero associated type so we can have niche optimization with arbitrary indices.
• The main Portgraph impl is still only done for <N=u32, P=u32>. I'll check if we can actually make the blanket impl next.

This may be a breaking change due to the new Unsigned::NonZero. I would hope users are not implementing that trait, but we forgot to seal it so we may need to mark this as breaking :/

[codspeed-hq]

Merging this PR will degrade performance by 15.17%

⚡ 1 improved benchmark
❌ 1 regressed benchmark
✅ 49 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	clone_line_graph[10000]	654.2 µs	511 µs	+28.02%
❌	clone_line_graph[1000000]	43 ms	50.7 ms	-15.17%

---

_{Comparing ab/node-meta-generic (f320844) with main (b1c2ab5)}

[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

    Building portgraph v0.15.3 (current)
     Built [  10.357s] (current)
   Parsing portgraph v0.15.3 (current)
    Parsed [   0.046s] (current)
  Building portgraph v0.15.3 (baseline)
     Built [   6.647s] (baseline)
   Parsing portgraph v0.15.3 (baseline)
    Parsed [   0.037s] (baseline)
  Checking portgraph v0.15.3 -> v0.15.3 (assume minor change)
   Checked [   0.064s] 196 checks: 194 pass, 2 fail, 0 warn, 56 skip

--- failure trait_associated_type_added: non-sealed public trait added associated type without default value ---

Description:
A non-sealed trait has gained an associated type without a default value, which breaks downstream implementations of the trait
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-new-item-no-default
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/trait_associated_type_added.ron

Failed in:
trait associated type portgraph::index::Unsigned::NonZero in file /home/runner/work/portgraph/portgraph/PR_BRANCH/src/index.rs:457

--- failure trait_method_added: pub trait method added ---

Description:
A non-sealed public trait added a new method without a default implementation, which breaks downstream implementations of the trait
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-new-item-no-default
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.47.0/src/lints/trait_method_added.ron

Failed in:
trait method portgraph::index::Unsigned::to_nonzero in file /home/runner/work/portgraph/portgraph/PR_BRANCH/src/index.rs:470
trait method portgraph::index::Unsigned::to_nonzero_unchecked in file /home/runner/work/portgraph/portgraph/PR_BRANCH/src/index.rs:477
trait method portgraph::index::Unsigned::from_nonzero in file /home/runner/work/portgraph/portgraph/PR_BRANCH/src/index.rs:480

   Summary semver requires new major version: 2 major and 0 minor checks failed
  Finished [  18.628s] portgraph

[aborgna-q]

The changes to PortEntry broke serialization. I'll update the impl there.