Add 12M swe-zero dataset

[neubig]

https://huggingface.co/datasets/AlienKevin/SWE-ZERO-12M-trajectories
Follow the patterns of previous work.

[openhands-ai]

I'm on it! neubig can track my progress at all-hands.dev

[openhands-ai]

Since my last summary, there have been no additional code changes.

Checklist:

• ✅ Issue Add 12M swe-zero dataset #257 (“Add 12M swe-zero dataset”) was completely addressed.
• ✅ Added the SWE-ZERO-12M dataset following existing dataset patterns.
• ✅ Generated required raw, standardized, and OpenHands v0 SFT sample files.
• ✅ Ran focused dataset validation tests successfully.
• ✅ Ran the full test suite successfully.
• ✅ Created branch openhands/add-swe-zero-12m.
• ✅ Committed and pushed the changes.
• ✅ Opened PR Add SWE-ZERO 12M dataset #258: Add SWE-ZERO 12M dataset #258
• ✅ PR description closes the issue and includes source, license, split, schema mapping, design decisions, limitations, and tests run.
• ✅ Changes are concise and scoped to the requested dataset addition; no extraneous files or unrelated changes were left in the working tree.