ssa fix slice high, update bytealg for pkg bytes/strings

[visualfc]

• ssa: fix slice high
• internal/lib/internal/bytealg: count index
• cl/_testlibgo: bytes strings

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.60%. Comparing base (8aed4d6) to head (8169d85).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #428 +/- ## ======================================= Coverage 97.60% 97.60% ======================================= Files 19 19 Lines 4138 4138 ======================================= Hits 4039 4039 Misses 82 82 Partials 17 17 ```

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