feat(streaming): add Identity as Content-Encoding for streamText()

[yusukebe]

Closes #3449

The author should do the following, if applicable

• Add tests
• Run tests
• bun run format:fix && bun run lint:fix to format the code
• Add TSDoc/JSDoc to document the code

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.58%. Comparing base (f1ec415) to head (9ff92eb).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3476   +/-   ##
=======================================
  Coverage   95.58%   95.58%           
=======================================
  Files         155      155           
  Lines        9357     9358    +1     
  Branches     2746     2843   +97     
=======================================
+ Hits         8944     8945    +1     
  Misses        413      413           

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[yusukebe]

Hey @sor4chi

Can you review this?

[sor4chi]

I think this header setting isn’t overridable. Is it OK?

it('Content-Encoding should be able to override', async () => {
  c.header('Content-Encoding', 'gzip')

  const res = streamText(c, async (stream) => {
    await stream.write('test')
  })

  expect(res.headers.get('content-encoding')).toBe('gzip') // should be gzip, but got identity
})

[yusukebe]

See #3449 (comment). Closing.