Turn SchemaSerializer into SchemaRegistry

[MattToast]

Rename SchemaSerializer to SchemaRegistry. Move Message formatting into a dedicated _Message class. Rename methods. Better error handling.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.68182% with 17 lines in your changes are missing coverage. Please review.

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Additional details and impacted files

@@             Coverage Diff             @@
##             protodrg       #8   +/-   ##
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  Coverage            ?   84.33%           
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  Files               ?       71           
  Lines               ?     4418           
  Branches            ?        0           
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  Hits                ?     3726           
  Misses              ?      692           
  Partials            ?        0           

Files	Coverage Δ
smartsim/_core/schemas/dragonRequests.py	97.22% <100.00%> (ø)
smartsim/_core/schemas/dragonResponses.py	100.00% <100.00%> (ø)
smartsim/_core/schemas/utils.py	100.00% <100.00%> (ø)
smartsim/_core/utils/helpers.py	91.96% <ø> (ø)
smartsim/_core/launcher/dragon/dragonSockets.py	75.00% <75.00%> (ø)
smartsim/_core/launcher/dragon/dragonLauncher.py	29.03% <16.66%> (ø)

[al-rigazzi]

One grammar nitpick to go!

[al-rigazzi]

Like it! LGTM, pending @ankona's approval.

[ankona]

LGTM!