Dump max_logic_levels as null if it isn't set (not to 0)

[gigeresk]

No description provided.

[greptile-apps]

Greptile Summary

The PR changes target_ppa_json to serialize an unset max_logic_levels constraint as JSON null rather than 0, while avoiding mutation of the global variable.

• Uses a local serialization value when the global constraint exists.
• Emits the JSON literal null when the constraint is absent.
• Removes incidental trailing whitespace.

Confidence Score: 5/5

The PR appears safe to merge with no actionable defects identified.

The changed procedure preserves configured numeric values, emits valid JSON null for the intended unset state, and no repository or related-repository code depends on the removed global-initialization side effect.

Important Files Changed

Filename	Overview
tcl/Extras.tcl	Correctly distinguishes an unset logic-level constraint from an explicit numeric value without introducing a concrete contract or runtime failure.

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