Replace SQLite with JSONL for client-side fallback buffer

[abidlabs]

Summary

• Replace SQLite with append-only JSONL files for the client-side fallback buffer (used when the remote Trackio Space is unreachable during training)
• SQLite's file locking and WAL journal mode break on networked filesystems like Lustre, causing sqlite3.DatabaseError: database disk image is malformed during distributed training on /fsx
• JSONL needs no locking, no journal mode, and no pragma configuration -- append-only writes are safe on any filesystem
• All _persist_*_locally methods are now wrapped in try/except so a storage failure can never kill the background logging thread

Context

A distributed training run on 8 GPUs crashed when trackio's remote logging hit QueueError: Queue is full! and the local SQLite fallback hit a corrupted database on Lustre. While the SQLite corruption didn't cause the training crash itself (that was a separate SIGBUS from the filesystem), it did kill the background logging thread, causing all subsequent metrics to be silently lost.

Test plan

• All existing tests pass (102 passed, 16 skipped)
• Test fallback path: start a run with space_id, make remote server unreachable, verify JSONL files are created in ~/.cache/huggingface/trackio/pending/
• Test flush path: reconnect server, verify buffered metrics are sent and JSONL files are cleaned up
• Test on networked filesystem (Lustre/NFS) with multiple concurrent writers

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🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
trackio	minor

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• Replace SQLite with JSONL for client-side fallback buffer

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Install Trackio from this PR (includes built frontend)

pip install "https://huggingface.co/buckets/trackio/trackio-wheels/resolve/bab9d8d0212bfdac65ae858e97527c155b070bac/trackio-0.22.0-py3-none-any.whl"

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