Server API refactor

[tmaxmax]

As part of the overhaul for v1 this brings many refactors to the server-side part of the library. See commits and changelog for information.

[codecov]

Codecov Report

Patch coverage: 88.29% and project coverage change: -2.02 ⚠️

Comparison is base (b0a45c4) 95.72% compared to head (4187103) 93.70%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #11      +/-   ##
==========================================
- Coverage   95.72%   93.70%   -2.02%     
==========================================
  Files          13       14       +1     
  Lines        1029     1096      +67     
==========================================
+ Hits          985     1027      +42     
- Misses         34       51      +17     
- Partials       10       18       +8     

Impacted Files	Coverage Δ
message.go	84.91% <ø> (+0.98%)	⬆️
session.go	72.22% <72.22%> (ø)
server.go	86.58% <85.33%> (-7.17%)	⬇️
replay_provider.go	91.42% <90.74%> (-8.58%)	⬇️
joe.go	96.35% <94.36%> (-2.86%)	⬇️
replay_buffer.go	96.29% <100.00%> (-3.71%)	⬇️
replay_noop.go	100.00% <100.00%> (ø)

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