feat: don't auto detect charset when using raw content parser option

[jerjako]

When the content is sent as raw, the charset can sometimes return a wrong value.
In this text example with Japanese characters, the charset content returning was iso-8859-1.

[coveralls]

coverage: 86.199%. remained the same
when pulling f25733f on jerjako:feat/dont-auto-detect-charset-for-raw-content
into c35a936 on jhillyerd:main.

[jhillyerd]

Thank you!