Fix Clippy Lints for Rust 1.88

[IvanIsCoding]

Related to #1471

Right now, the lints are disabled. This PR actually fixes them. Most of the fixes were automated following commands along the lines of:

cargo clippy --fix --lib -p rustworkx 

[coveralls]

Pull Request Test Coverage Report for Build 15950552464

Details

• 39 of 50 (78.0%) changed or added relevant lines in 16 files are covered.
• 72 unchanged lines in 19 files lost coverage.
• Overall coverage decreased (-0.6%) to 94.619%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
rustworkx-core/src/err.rs	0	1	0.0%
src/graph.rs	5	6	83.33%
src/graphml.rs	9	10	90.0%
src/json/mod.rs	1	2	50.0%
src/steiner_tree.rs	0	1	0.0%
src/json/node_link_data.rs	0	2	0.0%
rustworkx-core/src/dag_algo.rs	0	4	0.0%

Files with Coverage Reduction	New Missed Lines	%
rustworkx-core/src/centrality.rs	1	98.59%
rustworkx-core/src/generators/random_graph.rs	1	70.28%
rustworkx-core/src/steiner_tree.rs	1	96.55%
src/coloring.rs	1	98.82%
src/connectivity/johnson_simple_cycles.rs	1	97.44%
src/layout/spring.rs	1	99.56%
rustworkx-core/src/connectivity/biconnected.rs	2	97.62%
src/isomorphism/vf2.rs	2	96.01%
src/toposort.rs	2	89.38%
rustworkx-core/src/token_swapper.rs	3	95.59%

Totals
Change from base Build 15890388565:	-0.6%
Covered Lines:	17760
Relevant Lines:	18770

---

💛 - Coveralls

[mtreinish]

LGTM, thanks for fixing this