fix: add explicit lifetime annotations to silence rust 1.94 warnings

[publicmatt]

the mismatched_lifetime_syntaxes lint now warns when elided lifetimes are inconsistent between &self and the return type. adds '_ to three return types in network_partitions.

When I tried to use this as a dependency, rustc gave the following errors:

warning: hiding a lifetime that's elided elsewhere is confusing
  --> vendor/graspologic-native/packages/network_partitions/src/leiden/neighboring_clusters.rs:64:17
   |
64 |     pub fn iter(&self) -> Iter<usize> {
   |                 ^^^^^     ^^^^^^^^^^^ the same lifetime is hidden here
   |                 |
   |                 the lifetime is elided here
   |
   = help: the same lifetime is referred to in inconsistent ways, making the signature confusing
   = note: `#[warn(mismatched_lifetime_syntaxes)]` on by default
help: use `'_` for type paths
   |
64 |     pub fn iter(&self) -> Iter<'_, usize> {
   |                                +++

warning: hiding a lifetime that's elided elsewhere is confusing
   --> vendor/graspologic-native/packages/network_partitions/src/network/compact_network.rs:155:9
    |
155 |         &self,
    |         ^^^^^ the lifetime is elided here
156 |         id: CompactNodeId,
157 |     ) -> CompactNodeItem {
    |          ^^^^^^^^^^^^^^^ the same lifetime is hidden here
    |
    = help: the same lifetime is referred to in inconsistent ways, making the signature confusing
help: use `'_` for type paths
    |
157 |     ) -> CompactNodeItem<'_> {
    |                         ++++

warning: hiding a lifetime that's elided elsewhere is confusing
   --> vendor/graspologic-native/packages/network_partitions/src/network/compact_network.rs:167:9
    |
167 |         &self,
    |         ^^^^^ the lifetime is elided here
168 |         id: CompactNodeId,
169 |     ) -> NeighborIterator {
    |          ^^^^^^^^^^^^^^^^ the same lifetime is hidden here
    |
    = help: the same lifetime is referred to in inconsistent ways, making the signature confusing
help: use `'_` for type paths
    |
169 |     ) -> NeighborIterator<'_> {
    |                          ++++

warning: `network_partitions` (lib) generated 3 warnings (run `cargo fix --lib -p network_partitions` to apply 3 suggestions)