Refactor monolithic PDF class into specialized components and add Letter page size constants

[Copilot]

• Analyze CI failure logs
• Identify root cause: newly added Letter constants flagged as unused
• Add ##NEEDED pragma to c_letter_width and c_letter_height constants
• Verify linting passes
• Verify all tests pass

Original prompt

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This section details on the original issue you should resolve

<issue_title>add more features and split into multiple classes</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes add more features and split into multiple classes #5

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[larshp]

@copilot check and fix errors from CI

[Copilot]

@copilot check and fix errors from CI

Fixed CI errors. The abaplint unused_variables rule was flagging the newly added Letter page size constants (c_letter_width and c_letter_height) as unused. Added ##NEEDED pragma to both constants since they are part of the public API for external use. Fixed in commit 1feae6d.