Add support for optional trailing slashes

[CathalMullan]

Code is a little messy - but seems to work fine. Really do need an actual parser here.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #153 will not alter performance

_{Comparing 20-consider-supporting-trailing-slashes (c31efae) with main (436e95e)}

Summary

✅ 16 untouched benchmarks

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.40698% with 33 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/expander.rs	78.28%	1 Missing and 32 partials :warning:

Files with missing lines	Coverage Δ
src/errors/route.rs	100.00% <100.00%> (ø)
src/parser.rs	97.34% <100.00%> (+0.64%)	:arrow_up:
src/expander.rs	77.56% <78.28%> (-3.27%)	:arrow_down:

... and 1 file with indirect coverage changes