[hf-xet v1.6.0] Stream shard finalization progress

Improvements

• Stream shard finalization progress via POST /v2/shards, so large-shard validation/commit is visible instead of blocking silently after upload
• Expose shard upload progress (validation, commit stages, completion) through upload progress tracking, including Python ShardUploadProgressReport
• Minor upload efficiency: avoid cloning xorb bytes before streaming
• Reduce xet_session future size to avoid compilation failure and stack overflows
• Allow selecting the reqwest TLS backend via hf-xet features
• Drop pyo3 auto-initialize feature to avoid build failures when that feature is combined with a Python built --disable-shared

New Contributors

• @Expyron made their first contribution in #900

Full Changelog: v1.5.2...v1.6.0