vendor._gowin: implement lib.io buffer primitives.

[wanda-phi]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.37%. Comparing base (6857daf) to head (c4e39b8).
Report is 6 commits behind head on main.

❗ Current head c4e39b8 differs from pull request most recent head 99f9175. Consider uploading reports for the commit 99f9175 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1290      +/-   ##
==========================================
- Coverage   90.56%   90.37%   -0.20%     
==========================================
  Files          44       44              
  Lines       10638    10644       +6     
  Branches     2595     2538      -57     
==========================================
- Hits         9634     9619      -15     
- Misses        818      836      +18     
- Partials      186      189       +3     

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[whitequark]

LGTM. This is basically the same as ECP5.