Add comprehensive test coverage and example configuration for X-Forwarded-For

[Copilot]

Existing XFF tests covered basic functionality but lacked edge case validation and practical configuration examples.

Test Coverage

Added 10 tests across two new test classes:

TestXFFEdgeCases - Validates handling of:

• Malformed headers (empty, whitespace-only, invalid IPs)
• IPv6 addresses in X-Forwarded-For and xff_upstream_ip CIDR
• Whitespace handling in comma-separated IP lists
• Integration with other rule conditions (headers, user_agent)
• Rules without source_ip restrictions

TestXFFDocumentationScenarios - Validates:

• Load balancer scenario from README Example 7
• Multi-network access patterns

Example Configuration

Added rules/xff_example.yaml demonstrating:

• Source IP restrictions behind a proxy/load balancer
• Multiple CIDR ranges with XFF enabled
• Configuration comments and security warnings

rule:
  path: files/protected_xff_example.txt
  request_uri: /protected-xff
  source_ip:
    - 203.0.113.0/24   # External client network
    - 198.51.100.0/24
    - 192.0.2.50/32

Total test count: 47 → 57 tests, all passing.

Original prompt

Please update the test code to cover use_xff and xff_upstream_ip functionality, including the addition of a new example rules file to demonstrate how it can be configured.

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