Add eager encoding of keys and values

[sunsided]

Shifts the load of percent-encoding values to the construction of the string. Allows for cheaper reuse of the same builder, but incurs higher resource usage when building.

[codecov]

Codecov Report

❌ Patch coverage is 89.13043% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.03%. Comparing base (ccc3768) to head (627a766).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib.rs	89.13%	10 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main       #9      +/-   ##
===========================================
- Coverage   100.00%   96.03%   -3.97%     
===========================================
  Files            1        1              
  Lines          174      252      +78     
===========================================
+ Hits           174      242      +68     
- Misses           0       10      +10     

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