Fix curl command for text bodies starting with at sign

[cyphercodes]

What

Fix the generated debug curl command for text request bodies that begin with @.

Why

curl --data $'@filename\n' treats the value as a filename and fails before sending the request. For text bodies starting with @, the generated command now uses --data-raw so curl sends the literal body.

Fixes #5154

Tests

• cargo fmt --check
• cargo test -p hurl http::curl_cmd --lib
• ./target/debug/hurl --verbose build/repro-5154.hurl (local repro; verified generated command contains --data-raw $'@filename\\n' and not --data $'@filename\\n')

[lepapareil]

/rebase

[hurl-bot]

🕗 /rebase is running, please wait for completion.

[hurl-bot]

🔨 Auto rebase from Orange-OpenSource/hurl/master succeeds, cyphercodes/hurl/cyphercodes/fix-5154-curl-data-raw now embeds these commits:

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