submission update: zero-overlap placement with improved average wirelength

[Mummanajagadeesh]

This PR updates my placement submission and leaderboard entry.

What changed

• Implemented differentiable overlap repulsion in placement.py
• Added candidate shelf search and tuned local refinement
• Added tiny-case wirelength search for small designs
• Kept runtime-safe paths for very large cases to avoid hangs on tests 11 and 12
• Updated my leaderboard row in README.md

Latest results

• First 10 tests: Average Overlap 0.0000, Average Wirelength 0.2916, Total Runtime 65.21s
• Full 12 tests: Average Overlap 0.0000, Average Wirelength 0.3076, Total Runtime 65.90s

Notes

• Prioritized zero overlap while improving wirelength
• Branch is main on my fork and this PR tracks that branch

[Mummanajagadeesh]

@vbtcl

updated the implementation/results and wanted to check whether submissions are still being reviewed for the 2026 ML Sys internship challenge. thanks