perf: use NonZeroU32 for query and fragment start

[DonIsaac]

Closes #930 and addresses feedback #931.

Reduces Url memory layout from 88 bytes to 80 bytes.

[codecov]

Codecov Report

Attention: Patch coverage is 68.00000% with 24 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@54346fa). Learn more about missing BASE report.

Files	Patch %	Lines
url/src/lib.rs	62.29%	23 Missing ⚠️
url/src/parser.rs	85.71%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #933   +/-   ##
=======================================
  Coverage        ?   81.78%           
=======================================
  Files           ?       21           
  Lines           ?     3574           
  Branches        ?        0           
=======================================
  Hits            ?     2923           
  Misses          ?      651           
  Partials        ?        0           

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[DonIsaac]

@valenting may I please have a review on this?