Use same automatic encoding detection for all contents

[benoit74]

Fix #301

Changes:

• revisit decode of WARC content from bytes to string
  • only HTML content was benefiting from automatic encoding detection.
  • CSS used custom tinycss detection method
  • now, all content type (HTML, JS, CSS and JSON) use the same automatic encoding detection.
• add test cases around handling of encoding by the generic rewriter

[codecov[bot]]

Codecov Report

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

Project coverage is 83.89%. Comparing base (25b2804) to head (be3c0e3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #302 +/- ## ========================================== + Coverage 83.72% 83.89% +0.16% ========================================== Files 13 13 Lines 1223 1223 Branches 232 232 ========================================== + Hits 1024 1026 +2 + Misses 153 152 -1 + Partials 46 45 -1 ```

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