Make nts parsing independent of ntp-proto.

[davidv1992]

This is intended to be a rewrite of the main handling, providing a new starting point for refining the behavior. The old code was a PoC and it shows in the areas touched here, doing some stuff that was questionable.

[codecov]

Codecov Report

Attention: Patch coverage is 83.17089% with 259 lines in your changes missing coverage. Please review.

Project coverage is 67.34%. Comparing base (ea56d4a) to head (6eb5035).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib.rs	0.00%	184 Missing ⚠️
src/nts/mod.rs	94.21%	45 Missing ⚠️
src/nts/record.rs	95.34%	26 Missing ⚠️
src/config.rs	78.94%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            main       #5       +/-   ##
==========================================
+ Coverage   7.80%   67.34%   +59.54%     
==========================================
  Files          5        7        +2     
  Lines        628     1969     +1341     
==========================================
+ Hits          49     1326     +1277     
- Misses       579      643       +64     

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[squell]

Most changes LGTM but I have some remarks wrt. process. Also I really prefer the more detailed comment about connection re-use to be left in.