feat: allow for custom response parser with parseResponse

[chrstnfrrs]

Closes #13

Description

This PR allows for automatic response parsing to be disabled. This can be accomplished through passing { parse: false } into fetch options.

This PR also allows for custom parsing functions to be used. For example, JSON.parse can be used by passing { parse: JSON.parse } into fetch options.

Parsing still defaults to destr.

[Atinux]

Thank you for the PR @chrstnfrrs

Do you mind adding test cases in https://github.com/unjs/ohmyfetch/blob/main/test/index.test.ts?

[codecov-commenter]

Codecov Report

Merging #16 (3982d0d) into main (bb975a1) will increase coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
+ Coverage   98.30%   98.43%   +0.13%     
==========================================
  Files           4        4              
  Lines          59       64       +5     
  Branches       13       18       +5     
==========================================
+ Hits           58       63       +5     
  Misses          1        1              

Impacted Files	Coverage Δ
src/fetch.ts	97.56% <100.00%> (+0.33%)	⬆️

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[chrstnfrrs]

@Atinux I added two tests. I'm not super satisfied with the current test for the { parse: false } option due to the assertion not being on the piece of code under test. I can try to improve this over the weekend, but feel free to merge as-is.

[Atinux]

Will wait for Pooya to see if he spots any issue in the code

[pi0]

Thanks for contributing 💚 I have made a few adjustments to API to simplify