Iterate ParseIter during Bench

[attackgoat]

PR #11 did not iterate through the parsed characters, which produced inaccurate bench results. This PR:

• [x] Fixes the iteration
• [x] Updates criterion
• [x] Fixes some clippy lints
• [x] Makes a few unwraps quicker (2-5% gain)

Updated results compared to pre-#11 run from a different machine:

• Winner: Attackgoat: Before=1.3us After=455ns
• Van Gogh my earlo...[~520 CHARS]: Before=35us After=16.7us

This is the perf graph for Winner: Attackgoat; blue is this PR and red is d47fc1e with f8918b7:

I noticed this discrepancy when performance profiling some other code. This library is still fast but I was expecting more from the previous PR.