V6 builder

[constantoine]

Replace Totp::new and the likes with a builder pattern

[codecov]

Codecov Report

❌ Patch coverage is 93.57977% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.05%. Comparing base (c87d21e) to head (82f5f8e).

Files with missing lines	Patch %	Lines
src/algorithm.rs	48.64%	19 Missing ⚠️
src/url.rs	91.74%	9 Missing ⚠️
src/lib.rs	95.00%	3 Missing ⚠️
src/error.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##           v6_rewrite      #83      +/-   ##
==============================================
- Coverage       93.26%   93.05%   -0.21%     
==============================================
  Files               6        8       +2     
  Lines            1128     1094      -34     
==============================================
- Hits             1052     1018      -34     
  Misses             76       76              

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[constantoine]

TODO: Backport fixes from #82 before merging

Done