Fix calcuration size of Ext format

[shamaton]

If you have already use Ext Encoder/Decoder, you must add def.Byte1 to your encoder's CalcByteSize.

[codecov]

Codecov Report

❌ Patch coverage is 94.16667% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.51%. Comparing base (8b38235) to head (af3ecf2).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/encoding/encoding.go	83.63%	6 Missing and 3 partials ⚠️
internal/encoding/struct.go	55.55%	2 Missing and 2 partials ⚠️
time/encode.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #48      +/-   ##
==========================================
+ Coverage   98.43%   98.51%   +0.08%     
==========================================
  Files          71       71              
  Lines        6696     6736      +40     
==========================================
+ Hits         6591     6636      +45     
+ Misses         82       77       -5     
  Partials       23       23              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.