Use Arc for shared data

[CathalMullan]

Not sure I prefer this: but want to see if it's much faster or not.

EDIT: 3%. But more importantly, easier to work with.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #151 will not alter performance

_{Comparing 150-consider-using-arc-for-shared-data-rather-than-hashmap (8133b7c) with main (044463d)}

Summary

✅ 16 untouched benchmarks

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

:white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/node/search.rs	0.00%	0 Missing and 1 partial :warning:
src/router.rs	0.00%	1 Missing :warning:

Files with missing lines	Coverage Δ
src/node/search.rs	78.71% <0.00%> (ø)
src/router.rs	87.68% <0.00%> (+1.76%)	:arrow_up: