refactor: move getCharset helper to only usage

[Phillip9587]

...and uses optional chaining. In theory it short-circuits faster and by that avoids the empty string allocation and .toLowerCase() call. But this is only in theory and probably highly optimized in engines.

Same ideas as @Ayoub-Mabrouk in #557.

[Copilot]

Pull request overview

Refactors charset extraction by moving the getCharset helper from the shared lib/utils.js module into lib/read.js, where it is exclusively used, and updating the implementation to use optional chaining to avoid unnecessary string work when no charset is present.

Changes:

• Remove getCharset (and its content-type dependency) from lib/utils.js exports.
• Add a local getCharset implementation to lib/read.js and inline the content-type dependency there.
• Switch charset normalization to charset?.toLowerCase() to avoid allocating '' and lowercasing when charset is absent.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
lib/utils.js	Removes getCharset helper and the content-type import from the shared utils export surface.
lib/read.js	Adds content-type dependency and reintroduces getCharset locally for request charset parsing.

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