chore!: export codec methods

[evan-forbes]

Overview

If the methods for the Codec interface are exported, then users can define their own interfaces outside of this package. I'm not sure if leaving the methods unexported was done on purpose, so if it was this PR can be closed.

edit: for posterity this PR exported only a few methods, so it looks like it wasn't done on purpose, but I'm still unsure if there are any other specific reasons not to

Checklist

• New and updated code has appropriate documentation
• New and updated code has new and/or updated testing
• Required CI checks are passing
• Visual proof for any user facing features like CLI or documentation updates
• Linked issues closed with keywords

[codecov]

Codecov Report

Merging #195 (3a98be8) into master (f0b3545) will not change coverage.
The diff coverage is 60.00%.

❗ Current head 3a98be8 differs from pull request most recent head 25e11e5. Consider uploading reports for the commit 25e11e5 to get more accurate results

@@           Coverage Diff           @@
##           master     #195   +/-   ##
=======================================
  Coverage   81.15%   81.15%           
=======================================
  Files           7        7           
  Lines         520      520           
=======================================
  Hits          422      422           
  Misses         58       58           
  Partials       40       40           

Impacted Files	Coverage Δ
codecs.go	50.00% <ø> (ø)
extendeddatasquare.go	73.62% <33.33%> (ø)
leopard.go	77.77% <100.00%> (ø)

[cmwaters]

Makes sense to me