fix: replace pydantic with msgspec

[Ravencentric]

This ends up giving us a 1.5x speed improvement

❯ hyperfine --warmup 1 ".\old\Scripts\python.exe test_nzb_old.py" ".\.venv\Scripts\python.exe test_nzb.py"
Benchmark 1: .\old\Scripts\python.exe test_nzb_old.py
  Time (mean ± σ):      6.042 s ±  0.295 s    [User: 5.752 s, System: 0.259 s]
  Range (min … max):    5.754 s …  6.413 s    10 runs

Benchmark 2: .\.venv\Scripts\python.exe test_nzb.py
  Time (mean ± σ):      3.902 s ±  0.019 s    [User: 3.624 s, System: 0.222 s]
  Range (min … max):    3.871 s …  3.930 s    10 runs

Summary
  .\.venv\Scripts\python.exe test_nzb.py ran
    1.55 ± 0.08 times faster than .\old\Scripts\python.exe test_nzb_old.py

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (0846a73) to head (d17e8b1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #8   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        10    -1     
  Lines          597       600    +3     
=========================================
+ Hits           597       600    +3     

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