Refactor priority logic.

[CathalMullan]

Some ideas I'd like to experiment with:

• make constrained nodes a distinct node kind, meaning they'll always run first?
• can we move the if statements during search time to const?
• consider calculating the maximum priority a branch can result in, meaning we can skip branches that can't override our max. (need a test to trigger this?)
• simplify calculation, maybe just consider depth first, then length?
• expose priority values in display?

UPDATE: Happy with our new approach. No more magic numbers.

Should really fill out the ARCHITECTURE file one of these days.

Managed to sneak in under 300 ns / 4 µs too, which is likely the last signifigant threshold we'll ever hit. (not cherry picked, I promise!)

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 189 lines in your changes missing coverage. Please review.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/delete.rs	14.86%	62 Missing and 1 partial ⚠️
src/search.rs	83.18%	25 Missing and 13 partials ⚠️
src/optimize.rs	69.23%	24 Missing ⚠️
src/state.rs	58.62%	24 Missing ⚠️
src/find.rs	48.83%	22 Missing ⚠️
src/display.rs	41.66%	8 Missing and 6 partials ⚠️
src/insert.rs	97.05%	1 Missing and 3 partials ⚠️

Files with missing lines	Coverage Δ
src/errors/delete.rs	92.85% <ø> (+6.19%)	⬆️
src/lib.rs	78.04% <ø> (+9.75%)	⬆️
src/node.rs	100.00% <100.00%> (ø)
src/parser.rs	98.24% <100.00%> (-0.02%)	⬇️
src/router.rs	97.19% <100.00%> (+1.13%)	⬆️
src/sorted.rs	93.75% <100.00%> (ø)
src/insert.rs	95.92% <97.05%> (-3.13%)	⬇️
src/display.rs	63.73% <41.66%> (-7.91%)	⬇️
src/find.rs	67.54% <48.83%> (-24.23%)	⬇️
src/optimize.rs	79.45% <69.23%> (-14.74%)	⬇️
... and 3 more

[codspeed-hq]

CodSpeed Performance Report

Merging #229 will improve performances by 9.94%

_{Comparing 228-improve-priority-logic (0016d73) with main (31ec191)}

Summary

⚡ 2 improvements
✅ 14 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	228-improve-priority-logic	Change
⚡	matchit benchmarks/wayfind	11.5 µs	10.9 µs	+4.7%
⚡	path-tree benchmarks/wayfind	63.9 µs	58.1 µs	+9.94%