Fix jsonable_encoder bytes and memoryview encoding

[qing30252-stack]

/claim #759

Summary

• Encode bytes as base64 strings by default in jsonable_encoder.
• Add memoryview support by converting it through bytes first.
• Add bytes_encoding="hex" support for callers that need hexadecimal output.
• Add regression tests for bytes, memoryview, nested values, hex output, and invalid encoding values.
  -Added JSON data for the Ministry of Education of China,a central government public institution.
  -File:'data/public_institutions/ministry_of_education_china.json'
  -Includes name (English & Chinese), type, country, established year, headquarters, website, and mission.

Validation

• python -m py_compile fastapi\encoders.py tests\test_jsonable_encoder.py
• python -m pytest tests\test_jsonable_encoder.py -q
• Valid JSON format confirmed.

Demo video

https://youtu.be/Q9B4Uv9HM2o

Fixes bounty #759

[github-actions]

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