[Performance] Optimize sanitizedHeadersOutput header sanitization

[gonzaloriestra]

WHY are these changes introduced?

sanitizedHeadersOutput is called frequently when verbose logging or unit testing HTTP and GraphQL API requests/responses. Previously, it performed multiple object allocations and redundant iterations:

1. Called header.toLowerCase() for every keyword in SENSITIVE_HEADERS inside a .find() callback on each header.
2. Built an intermediate sanitized object using forEach.
3. Extracted keys from sanitized with Object.keys() a second time to map into output strings.

WHAT is this pull request doing?

Refactors sanitizedHeadersOutput to use single-pass Object.entries(headers) filtering:

• Lowercases each header name once per entry and caches it locally.
• Short-circuits keyword checking using !SENSITIVE_HEADERS.some(...).
• Directly maps filtered key-value pairs into formatted strings without intermediate object allocations or duplicate Object.keys() lookups.

How to test your changes?

Run any CLI command with --verbose flag (e.g. shopify app info --verbose) or execute API-related tests.

Post-release steps

None.

Measuring impact

Status	File
OK	packages/cli-kit/src/private/node/api/headers.ts

Checklist

• I have read the Contributing Guidelines.
• I have read the CLI Reference Standard for UX compliance.
• I have included test coverage for new functionality or bug fixes.
• I have updated the documentation where necessary.
• I have tested my changes locally.
• I have verified that all CI checks pass.

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PR created automatically by Jules for task 2168919330683522285 started by @gonzaloriestra

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