content_encoding: avoid strcpy

[bagder]

Build list with dynbuf.

[bagder]

augment review

[Copilot]

Pull request overview

This PR refactors the content encoding list building to use dynamic buffers (dynbuf) instead of fixed-size buffers and strcpy operations. The changes improve memory safety by avoiding potential buffer overflows.

Key changes:

• Replaced Curl_all_content_encodings() with Curl_get_content_encodings() that returns a dynamically allocated string
• Eliminated fixed-size 256-byte stack buffer in favor of dynamic allocation
• Simplified error message to remove redundant encoding list generation

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
lib/content_encoding.h	Updated function signature to return CURLcode and use output parameter for string
lib/content_encoding.c	Refactored to build encoding list with dynbuf; simplified error message
lib/setopt.c	Updated caller to use new API with proper error handling

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[augmentcode]

🤖 Augment PR Summary

Summary: Refactors content-encoding name list generation to avoid fixed-size buffers/strcpy.

Changes:

• Adds `curlx/dynbuf.h` and builds the encoding list using `dynbuf`.
• Replaces `Curl_all_content_encodings(buf, blen)` with `Curl_get_content_encodings()` returning an allocated string.
• Updates `CURLOPT_ACCEPT_ENCODING` empty-string handling to use the new helper.
• Simplifies the error path for unknown content encoding messages.

Technical Notes: Callers now need to handle ownership of the returned string and OOM behavior.

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[augmentcode]

Review completed. 2 suggestions posted.

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