feat!: make 'flush' method on encoder consume 'self'

[danieleades]

closes #77

there is one downside to this approach i can immediately see, but it's a bit niche- a user cannot retry a write to an output buffer if writing fails during a call to 'flush'.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.51%. Comparing base (ad0ccb0) to head (9647548).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #79   +/-   ##
=======================================
  Coverage   76.51%   76.51%           
=======================================
  Files          11       11           
  Lines         596      596           
=======================================
  Hits          456      456           
  Misses        140      140           

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[danieleades]

@DCNick3 is this what you had in mind?

[DCNick3]

Yep, pretty much!