fix(mellea decomp): Solve ConstraintExtractor parsing fails and improve robustness

[csbobby]

[mellea decomp] Improve ConstraintExtractor parsing fails and improve robustness

Type of PR

• Bug Fix

Description

This PR improves the parsing logic in ConstraintExtractor (mellea decomp) to make constraint extraction more robust, less brittle to formatting variance, and safer under partial / malformed model outputs.

ConstraintExtractor currently relies on naive patterns (e.g., line formatting). In practice, LLM outputs vary across:
• bullet styles (-, *, 1.)
• inline constraints mixed with prose
• missing sections or merged sections
• multi-line constraints with continuation indentation

This leads to:
• false negatives (constraints missed)
• false positives (non-constraints treated as constraints)
• unstable behavior across models / temperatures

Key Changes:
1. Stricter N/A handling
• The extractor now returns an empty list only when the input, after trimming and uppercasing, exactly matches known N/A variants ("N/A", "N / A", "N/ A", "N /A").
• This avoids false positives where N/A appears as a substring within a longer, meaningful constraint description.
2. Line-based parsing with empty-line filtering
• Constraints are processed line by line with leading/trailing whitespace removed.
• Empty lines are skipped to prevent generating empty constraints.
3. Bullet and numbering removal
• Common bullet and numbering prefixes (e.g. -, *, •, 1., 1)) are stripped from each line to normalize constraint text.
4. Inline multi-constraint splitting
• Single lines containing multiple constraints are split using common separators such as ;, -, –, and —.
• Each extracted constraint is individually trimmed and validated before being added to the results.

Testing

• Tests added to the respective file if code was changed
• New code has 100% coverage if code as added
• Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

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