Instead of failing with 409 on version conflicts, use "first version wins"
strategy. This allows resolution to succeed for complex dependency trees
like tensorflow where transitive dependencies may have overlapping but
not identical version requirements.
The resolver now:
- Checks if an already-resolved version satisfies a new constraint
- If yes, reuses the existing version
- If no, logs the mismatch and uses the first-encountered version
This matches pip's behavior of picking a working version rather than
failing on theoretical conflicts.
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