[FIX] Preflight auth

[pdeziel]

Scope of changes

This fixes a bug in the preflight auth logic to ensure that the credentials are actually being supplied in the header after an endpoint requires preflight authentication. Previously, the self._request_headers was being overwritten since the preflight function is actually called twice for the first request, so this changes it to a local variable.

Type of change

• new feature
• bug fix
• documentation
• testing
• technical debt
• other (describe)

Acceptance criteria

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Definition of Done

• I have manually tested the change running it locally (having rebuilt all containers) or via unit tests
• I have added unit and/or integration tests that cover my changes
• I have added new test fixtures as needed to support added tests
• I have updated the dependencies list if necessary (including updating yarn.lock and/or go.sum)
• Check this box if a reviewer can merge this pull request after approval (leave it unchecked if you want to do it yourself)
• I have notified the reviewer via Shortcut or Slack that this is ready for review

Reviewer(s) checklist

• Any new user-facing content that has been added for this PR has been QA'ed to ensure correct grammar, spelling, and understandability.
• Are there any TODOs in this PR that should be turned into stories?

[Copilot]

Pull Request Overview

This PR fixes a bug in the preflight authentication logic where credentials were not being properly supplied in request headers. The issue occurred because the _pre_flight method was being called twice for the first request, causing self._request_headers to be overwritten.

• Changed _pre_flight method to return headers as a local variable instead of modifying instance state
• Updated all HTTP methods (GET, POST, PUT, DELETE) to use the returned headers directly
• Added comprehensive test coverage for the preflight authentication functionality

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
guidelight/client.py	Modified _pre_flight method to return headers locally and updated all HTTP methods to use returned headers
tests/test_client.py	Added new test file with preflight authentication test case
tests/requirements.txt	Added pytest-httpserver dependency for testing HTTP interactions

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[bbengfort]

Good catch!